Ionic liquid additive for lithium-ion battery

ABSTRACT

An ionic liquid additive for lithium-ion batteryAn ionic liquid for adding to an electrolyte of a lithium-ion battery, the ionic liquid comprises a compound with a dual core structure having the general formula (I):wherein each of cationic group X1 and X2 are heterocyclic aromatic and amine.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. Provisional Application No. 63/139,860, filed Jan. 21, 2021, the entire disclosure of which is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to an additive to an electrolyte for lithium-ion battery, in particular but not limited to an ionic liquid as an additive to the electrolyte.

BACKGROUND OF THE INVENTION

In recent years, the demand for batteries with high power, high energy density and long cyclic stability has increased with the rapid development of the application of lithium-ion batteries in power battery systems. Due to the continuous pursuit for high-energy density batteries, the use of electrodes with high-areal density and high-compaction density is currently one of the common methods in the industry. However, a resulting problem would be that the diffusion of lithium ions in the electrode becomes unsatisfactory. Furthermore, the interface impedance between the positive and negative electrodes increases, leading to greater polarization of the battery on the average voltage difference between charging and discharging curves, which makes the battery performance worse.

During the formation of lithium-ion batteries, a solid electrolyte interface (SEI) layer is formed on the surface of the anode, which controls the passage of lithium ions. When the formed SEI film is too thick and the impedance is high, lithium ions cannot migrate and penetrate, it will result in lithium precipitation. When the SEI film is not sufficiently dense and stable, it will dissolve gradually or may rupture during the charging and discharging processes, exposing the negative electrode and permitting its chemical reaction with the electrolyte. This brings about a continual decrease in the capacity of battery as the electrolyte is consumed by reacting with the negative electrode.

Another relatively prominent problem with lithium-ion batteries would be the increase of internal temperature of the battery due to improper heating, overcharging, puncture damage, etc. Puncture damage will result in short circuit when the positive and negative electrodes are in contact. It may not be possible to suppress the rise in internal temperature of the battery and this is likely to result in the decomposition of the SEI film and electrolytes. During the decomposition, H₂, O₂, HF, PF₅ and other active flammable compounds are produced. When the temperature rises to 200° C., the decomposition reaction of electrolytes and cathode materials will be occurred. Such decomposition reaction generates large amount of hydrogen, oxygen, and fluoride, leading to potential fire and explosion hazards. The performance and thermal safety of a lithium-ion battery depends on a lot which includes but not exclusively the cathode/anode materials, the property of the electrolyte as well as their relationship with the SEI layer on the surface of electrode.

An ionic liquid is a molten salt composed of anion and cation, which still exhibits a liquid state below 100° C. It has low volatility, high melting point, high ionic conductivity, a wide potential window and is a good flame retardant. With the aforementioned, it is a reasonable candidate of electrolyte additives for lithium-ion batteries. However, most of the ionic liquids are readily intercalated into the layer structure of graphite on the surface of the anode during the battery charging process, thereby increasing the impedance resistance of the SEI layer and results in severe generation of lithium precipitation. The resulting battery exhibits poor cyclic performance. Even with the presence of film-forming agent and stabilizer, inhibition of the intercalation effect is limited and the generation of the lithium precipitation is unavoidable.

SUMMARY OF THE INVENTION

In the first aspect of the invention there is provided an ionic liquid for adding to an electrolyte of a lithium-ion battery, the ionic liquid comprises a compound with a dual core structure having the general formula (I):

-   -   wherein each of cationic group X₁ and X₂ are heterocyclic         aromatic and amine. Preferably, the heterocyclic aromatic is         selected from a group consisting piperidinium, pyrrolidinium,         pyrazolium and pyridinium.     -   More preferably, the amine is selected from a group consisting         quaternary ammonium, azepane and phosphonium.     -   Yet more preferably, X₁ and X₂ is selected from a group         consisting of:

-   1,5 Bis(1-methylpyrrolidium 1-yl) pentane

-   1,5 Bis(1-methylpiperidinium 1-yl) pentane

-   1,5 (1-methylpyrrolidium 1-yl) (1-methylpiperidinium 1-yl) pentane

-   1,5-[(1-methylpyrrolidium 1-yl) (triethylamine N-yl)] pentane

-   1,5-[(1-methylpiperidinium 1-yl) (triethylamine N-yl)] pentane

Preferably, the heterocyclic aromatic does not include imidazolium and morpholinium.

-   -   More preferably, X₁ and X₂ comprises two different functional         group.     -   Yet more preferably, Y is any one of C3˜C10 alkyl group.     -   Advantageously, X₁YX₂ is selected from a group consisting:

-   1,4 Bis(1-methylpyrrolidium 1-yl) butane

-   1,5 Bis(1-methylpyrrolidium 1-yl) pentane

-   1,6 Bis(1-methylpyrrolidium 1-yl) hexatane

-   1,8 Bis(1-methylpyrrolidium 1-yl) octane     -   More advantageously, Y is selected from a group consisting of         sulfonyl, carbonic acid, ether, ketone group and ester.     -   Yet more advantageously, X₁YX₂ is selected from a group         consisting:

-   Bis [2-(1-methylpyrrolidinium 1-yl) ethyl] ether

-   Bis [2-(1-methylpyrrolidinium 1-yl) ethyl] carbonate

-   1,5-Bis(1-methylpyrrolidinium 1-yl) pentan-3-one

-   Bis[2-(1-methylpyrrolidinium 1-yl) ethyl] butanedioate     -   Preferably, the anionic group Z₁ and Z₂ os selected from a group         consisting: PF₆ ⁻ (hexafluorophosphate), POF₂ ⁻         (difluorophosphate), BF₄ ⁻ (tetrafluoroborate), B(C₂O₄)₂ ⁻         (BOB⁻, bis(oxalato) borate), BF₂(C₂O₄)⁻ (ODFB⁻,         difluoro(oxalato)borate), CF₃BF₃ ⁻         (trifluoromethyltrifluoroborate), (FSO₂)₂N⁻ (FSI⁻,         bis(fluorosulfonyl)imide), (CF₃SO₂)₂N⁻ (TFSI⁻,         bis(trifluoromethane)sulfonamide), CH₃SO₄ ⁻ (MeSO₄ ⁻, methyl         sulfate).     -   In a second aspect of the invention there is provided an ionic         liquid for adding to an electrolyte of a lithium-ion battery,         the ionic liquid comprises a compound with a dual core structure         having the general formula (I):

-   -   wherein each of cationic group X₁ and X₂ are heterocyclic         aromatic and amine.     -   Preferably, the heterocyclic aromatic is selected from a group         consisting piperidinium, pyrrolidinium, pyrazolium and         pyridinium.     -   More preferably, the amine is selected from a group consisting         quaternary ammonium, azepane and phosphonium.     -   Yet more preferably, Y is any one of C3˜C10 alkyl group.     -   It is preferable that Y is selected from a group consisting of         sulfonyl, carbonic acid, ether, ketone group and ester.     -   Advantageously, X₁YW is selected from a group consisting:

-   Benzyl-2-(1-methylpyrrolidinium 1-yl) ethyl ether

-   Benzyl-4-(1-methylpyrrolidinium 1-yl) butyl ether

-   1-(1-Benzoyl)-1-methyl pyrrolidinium

-   1-(2-Phenacyl)-1-methyl pyrrolidinium

-   1-(Furan 2-yl)-1-methyl pyrrolidinium

-   1-(butyl furan 2-yl)-1-methyl pyrrolidinium

-   1-(2-Furoyl)-1-methyl pyrrolidinium

-   1-Benzensulfonyl-1-methyl pyrrolidinium

-   -   1-p-Toluenesulfonyl-1-methyl pyrrolidinium     -   More advantageously, the anionic group Z₁ and Z₂ of the ionic         liquid with structural formula I and formula II can include PF₆         ⁻ (hexafluorophosphate), POF₂ ⁻ (difluorophosphate), BF₄ ⁻         (tetrafluoroborate), B(C₂O₄)₂ ⁻ (BOB⁻, bis(oxalato) borate),         BF₂(C₂O₄)⁻ (ODFB⁻, difluoro(oxalato)borate), CF₃BF₃ ⁻         (trifluoromethyltrifluoroborate), (FSO₂)₂N⁻ (FSI⁻,         bis(fluorosulfonyl)imide), (CF₃SO₂)₂N⁻ (TFSI⁻,         bis(trifluoromethane)sulfonamide), CH₃SO₄ ⁻ (MeSO₄ ⁻, methyl         sulfate).     -   In a third aspect of the invention there is provided a lithium         ion battery comprising a positive electrode, a negative         electrode, a separator, an electrolyte and one or more ionic         liquid disclosed herein, wherein an overall amount of ionic         liquid added to the electrolyte is 0.1-15 wt. %.     -   Preferably, the lithium ion battery further comprising a         stabilizer, wherein the stabilizer is a cyclophosphazene         compound.     -   More preferably, the stabilizer is selected from a group         consisting:

-   Hexafluoro cyclotriphosphazene

-   Ethoxy (pentafluoro) cyclotriphosphazene     -   Yet more preferably, amount of stabilizer added to the         electrolyte is 0.1-2.9 wt. %.     -   It is preferable that a SEI film forming agent is added to the         electrolyte.     -   Advantageously, the SEI film forming agent is selected from a         group consisting of fluoroethylene carbonate (FEC), vinylene         carbonate (VC), vinyl ethylene carbonate (VEC), ethylene sulfite         (ES), propylene sulfite (PS), and ethylene sulfate (DTD), and         the combination thereof.     -   More advantageously, the amount of the SEI film forming agent         added to the electrolyte is 0.1-5 wt. %.     -   More advantageously, the electrolyte is an non-aqueous         electrolyte.     -   Yet more advantageously, the non-aqueous electrolyte comprises a         lithium salt selected from a group consisting of LiPF₆, LiClO₄,         LiBF₄, LiSO₃CF₃, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, LiN(SO₂CF₂CF₃)₂,         LiAsF₆, LiAlCl₄, LiNO₃, LiPOF₂, LiB(C₂O₄)₂, LiBF₂(C₂O₄),         LiCF₃BF₃, or a combination thereof.     -   Preferably, concentration of the lithium salt in the electrolyte         is 0.5˜1.5 mol/L.     -   More preferably, the nonauqeous electrolyte comprises an organic         solvent selected from a group consisting of carbonate,         carboxylate, ether, ketone, and combinations thereof     -   More preferably, the carbonate is selected from a group         consisting ethylene carbonate (EC), propylene carbonate (PC),         diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl         carbonate (DMC), dipropyl carbonate, dibutyl carbonate, and a         combination thereof.     -   Preferably, the carboxylate is carboxylic acid ester.     -   More preferably, the carboxylic acid ester comprises methyl         acetate, ethyl acetate, methyl butyrate, ethyl butyrate, methyl         propionate, ethyl propionate and propyl acetate, and a         combination thereof.     -   It is preferable that the positive electrode comprises an active         material being lithium metal complex oxide compound.     -   It is preferable that the metal element of the lithium metal         complex oxide is selected from a group consisting of transition         metal and non-transition metal.     -   Preferably, the transition metal is selected from a group         consisting vanadium, titanium, chromium, copper, iron, nickel         and cobalt.     -   More preferably, the non-transition metal is selected from a         group consisting aluminum and manganese.     -   Yet more preferably, the negative electrode comprises an active         material selected from a group consisting soft carbon, hard         carbon, artificial graphite, natural graphite, meso carbon micro         bead (MCMB), silicon, silicon oxide compounds, silicon carbon         composites, lithium titanate oxide, and the metals that forms         alloy with lithium.     -   It is preferable that the negative electrode comprises an active         material that is carbon-based, silicon-based or tin-based.     -   Advantageously, the separator comprises a membrane.     -   More advantageously, the membrane comprises a material selected         form a group consisting polyethylene (PE), polypropylene (PP),         polyvinylidene fluoride (PVDF), ceramic material, glass fiber         and a combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a table that shows the synthesis parameters of bis(1-methylpyrrolidium) alkyl halide;

FIG. 2 is a table that shows the synthesis parameters of two-core cationic chain halide;

FIG. 3A is a table that shows the synthesis parameters of two-core cationic chain ionic liquid;

FIG. 3B is a continuation of the table in FIG. 3A;

FIG. 4 is a table that shows the synthesis parameters of aromatic bonded to 1-methylpyrrolidinium halide;

FIG. 5 is a table that shows the synthesis parameters of aromatic bonded to cation halide;

FIG. 6A is a table that shows the synthesis parameters of aromatic bonded to cation ionic liquid;

FIG. 6B is a continuation of the table in FIG. 6A;

FIG. 7A is a graph showing results of a liner sweep voltammetry LSV of PYR₁₃PF₆;

FIG. 7B is a graph showing the circled part in FIG. 7A in a different scale;

FIG. 8A is a graph showing results of a linear sweep voltammetry LSV of DiPYR₁₅(PF₆)₂;

FIG. 8B is a graph showing the reading of the circled part in FIG. 8A;

FIG. 9A is a graph showing results of a linear sweep voltammetry LSV of DiPYR₁₈(PF₆)₂;

FIG. 9B is a graph showing the reading of the circled part in FIG. 9A;

FIG. 10A is a graph showing results of a linear sweep voltammetry LSV of DiPYR_(IEE)(PF₆)₂;

FIG. 10B is a graph showing the reading of the circled part in FIG. 10A;

FIG. 11A is a graph showing results of a linear sweep voltammetry LSV of PYRPIP₁₅(PF₆)₂;

FIG. 11B is a graph showing the reading of the circled part in FIG. 11A;

FIG. 12A is a graph showing results of a linear sweep voltammetry LSV of DiPIP₁₅(PF₆)₂;

FIG. 12B is a graph showing the reading of the circled part in FIG. 12A;

FIG. 13A is a graph showing results of a linear sweep voltammetry LSV of DiPYR₁₅(PF₆)(BF₄);

FIG. 13B is a graph showing the reading of the circled part in FIG. 13A;

FIG. 14A is a graph showing results of a linear sweep voltammetry LSV of DiPYR₁₅(PF₆)(BF₄);

FIG. 14B is a graph showing the reading of the circled part in FIG. 14A;

FIG. 15A is a table showing the maximum oxidation potential of electrolyte with the two-core structure ionic liquid at the LSV test;

FIG. 15B is a continuation of the table in FIG. 15A;

FIG. 15C is a continuation of the table in FIG. 15A and FIG. 15B;

FIG. 16A is a table showing the maximum oxidation potential of electrolyte with aromatic bonded to cation ionic liquid at the LSV test;

FIG. 16B is a continuation of the table in FIG. 16A;

FIG. 17 is a graph showing results of a linear sweep voltammetry LSV of PYR₁₃PF₆;

FIG. 18A is a graph showing results of a linear sweep voltammetry LSV of Di PYR₁₅(PF₆)₂;

FIG. 18B is a graph showing results of a linear sweep voltammetry LSV of Di PYR₁₈(PF₆)₂;

FIG. 19A is a graph showing results of a linear sweep voltammetry LSV of DiPYR_(IEE)(PF₆)₂;

FIG. 19B is a graph showing results of a linear sweep voltammetry LSV of PIPPYR15(PF₆)₂;

FIG. 19C is a graph showing results of a linear sweep voltammetry LSV of DiPIP₁₅(PF₆)₂;

FIG. 19D is a graph showing results of a linear sweep voltammetry LSV of DiPYR₁₅(PF₆)(BF₄);

FIG. 20 is a graph showing results of Li₂CO₃ product, PYRTEA₁₅(PF₆)₂ added at 6 wt. % to the OE, DiPYR₁₅(PF₆)₂ added at 6 wt. % to the OE and DiPYR_(IEE)(PF₆)₂ added at 6 wt. % to the OE as well as an organic electrolyte (OE) being tested by X-ray absorption spectrum O K-edge TEY;

FIG. 21A is a table showing the composition of different electrolyte formulas;

FIG. 21B is a continuation of the table in FIG. 21A;

FIG. 22A shows a top plan view of a LFP battery (Lithium-ion battery) in accordance with the invention;

FIG. 22B shows a side view of the LFP batter in FIG. 22A;

FIG. 23A is a table showing results of the self-extinguishing time of various electrolyte formulations and its internal impedance and long-cycle performance of lithium-ion battery; and

FIG. 23B is a continuation of the table in FIG. 23A.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The first aspect of the invention relates to an ionic liquid with dual core cationic chain and aromatic functional group bonded to cation (dual core structure). It has a high melting point and a wide potential window, is not easy to intercalate into graphite layer of anode materials, and can form a solid electrolyte interface (SEI) with uniform, compact, and high lithium diffusion reversibility on the surface of the anode. The ionic liquid is added to the non-aqueous electrolyte, to enhance the long-term cyclic stability of the high compacted density electrode and improve the thermal stability of the resulting lithium ion battery.

The dual-core structure increases the structural volume of the cation much bigger such that it becomes too large for intercalation in graphite. A uniform and dense SEI layer is formed on the surface of graphite for reversible intercalation and release of lithium ions. This reduces the interface impedance and enhance the long-term cyclic stability for the lithium-ion battery. Furthermore, the SEI layer with high flame retardancy produced after adding the ionic liquid to the electrolyte can absorb internal heat and inhibit thermal runaway.

As discussed above, the dual core cation is characterized by an aromatic compound, amine salt and heterocyclic compound.

The second aspect of the invention involves the use of the ionic liquid in the first aspect of the invention with a non-aqueous electrolyte.

The third aspect of the invention is related to a lithium-ion battery with the non-aqueous electrolyte in the second aspect and the ionic liquid in the second aspect.

In more detail, the dual-core structure of ionic liquid has the two functional groups chain. It is made up of a dual-core cationic chain and an aromatic functional group bonded to cations in the dual-core cationic chain. The dual-core structure has a general formula of Z₁X₁YX₂Z₂ and Z₁X₁YW, with their chemical structural formulas shown below as structure I and structure II, respectively.

The cationic group X₁ and X₂ in structural formula I and the cationic group X₁ in structural formula II are selected from a group consisting heterocyclic aromatics and amine salt. The heterocyclic aromatics includes piperidinium, pyrrolidinium, pyrazolium and pyridinium, while the amine salt includes quaternary ammonium, azepane and phosphonium.

More specifically, the cationic group X₁ and X₂ in structural formula I and the cationic group X₁ in structural formula II are selected from:

-   1,5 Bis(1-methylpyrrolidium 1-yl) pentane,

-   1,5 Bis(1-methylpiperidinium 1-yl) pentane,

-   1,5 (1-methylpyrrolidium 1-yl) (1-methylpiperidinium 1-yl) pentane,

-   1,5-[(1-methylpyrrolidium 1-yl) (triethylamine N-yl)] pentane,     and/or

-   1,5-[(1-methylpiperidinium 1-yl) (triethylamine N-yl)] pentane.

The functional group Y of the ionic liquid with structural formula I and formula II is alkyl group, R indicates the number of carbon atom in the alkyl group, wherein the R=3-10 in particular it is selected from:

-   1,4 Bis(1-methylpyrrolidium 1-yl) butane,

-   1,5 Bis(1-methylpyrrolidium 1-yl) pentane,

-   1,6 Bis (1-methylpyrrolidium 1-yl) hexatane, and/or

-   1,8 Bis(1-methylpyrrolidium 1-yl) octane

The functional group Y of the ionic liquid with structural formula I and formula II is selected from sulfonyl, carbonic acid, ether, ketone group or ester. In particular, the function group Y is selected from:

-   Bis [2-(1-methylpyrrolidinium 1-yl) ethyl] ether,

-   Bis [2-(1-methylpyrrolidinium 1-yl) ethyl] carbonate,

-   1,5-Bis(1-methylpyrrolidinium 1-yl) pentan-3-one, and/or

-   Bis[2-(1-methylpyrrolidinium 1-yl) ethyl] butanedioate

The cationic group X₁, the functional group Y and the aromatic group W of the ionic liquid with structural formula II is selected from:

-   Benzyl-2-(1-methylpyrrolidinium 1-yl) ethyl ether,

-   Benzyl-4-(1-methylpyrrolidinium 1-yl) butyl ether,

-   1-(1-Benzoyl)-1-methyl pyrrolidinium,

-   1-(2-Phenacyl)-1-methyl pyrrolidinium,

-   1-(Furan 2-yl)-1-methyl pyrrolidinium,

-   1-(butyl furan 2-yl)-1-methyl pyrrolidinium,

-   1-(2-Furoyl)-1-methyl pyrrolidinium,

-   1-Benzensulfonyl-1-methyl pyrrolidinium, and/or

-   1-p-Toluenesulfonyl-1-methyl pyrrolidinium.

The anionic group Z₁ and Z₂ of the ionic liquid with structural formula I and formula II may include PF₆ ⁻ (hexafluorophosphate), POF₂ ⁻ (difluorophosphate), BF₄ ⁻ (tetrafluoroborate), B(C₂O₄)₂ ⁻ (BOB⁻, bis(oxalato) borate), BF₂(C₂O₄)⁻ (ODFB⁻, difluoro(oxalato)borate), CF₃BF₃ ⁻ (trifluoromethyltrifluoroborate), (FSO₂)₂N⁻ (FSI—, bis(fluorosulfonyl)imide), (CF₃SO₂)₂N⁻ (TFSI⁻, bis(trifluoromethane)sulfonamide), and/or CH₃SO₄ ⁻ (MeSO₄ ⁻, methyl sulfate).

The weight percentage of the ionic liquid in the electrolyte is 0.1-15 wt. %. When the added amount of ionic liquid is too low, the improvement effect of the electrolyte on the surface of anode is not obvious, but that is too high, the thickness of SEI layer formed will be much larger, consequently increases the interface impedance between the cathode and anode, resulting in the decline of battery performance.

The non-aqueous electrolyte, including lithium salt, organic solvent, film-forming agent, stabilizer and ionic liquid.

The stabilizer in the non-aqueous electrolyte is a cyclophosphazene compound, preferably selected from the followings:

Hexafluoro cyclotriphosphazene, and/or

Ethoxy (pentafluoro) cyclotriphosphazene.

The cyclophosphazene compound contains P and F which are both highly efficient flame retardants. The presence of P and F allow for reduction in the amount of ionic liquid to be added into the electrolyte with noticeable thermal stability advantage. F assists in generating more LiF on the SEI film formed on the surface of the electrode. The LiF on the SEI film acts as a good oxidation resister to increase the compatibility between the electrolyte and any active materials in the electrode by reducing the reaction between them and the production of unwanted by-product. This in turns stabilizes the electrochemical reaction of electrodes and improves the long term cyclic performance of lithium-ion batteries with high-voltage. The proposed amount of stabilizer in the electrolyte is 0.1-2.9 wt. %.

The SEI film forming agent in the non-aqueous electrolyte is selected from one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), ethylene sulfite (ES), propylene sulfite (PS), and ethylene sulfate (DTD).

The film-forming agent has a higher reduction potential and can be preferentially reduced as SEI film on the surface of the graphite electrode. The inorganic lithium compound containing sulfur and fluorine is more stable, and it is beneficial to the insertion and release of lithium ions, lower the reduction and decomposition rate of the electrolyte as well as the occurrence of undesirable side reaction on the surface of negative electrode. The preferred amount of SEI film-forming agent in the electrolyte is 0.1-5 wt. %. It is a fine balance. Too low an amount of the SEI film-forming agent will result insignificant improvement on the surface of the electrode, while too large an amount of the SEI film-forming agent results in undesirable thickening of the SEI film as this will affect the capacity retention of the battery which brings about a decline in the cyclic performance of the overall battery.

The lithium salt in the non-aqueous electrolyte includes any one of LiPF₆, LiClO₄, LiBF₄, LiSO₃CF₃, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, LiN(SO₂CF₂CF₃)₂, LiAsF₆, LiAlCl₄, LiNO₃, LiPOF₂, LiB(C₂O₄)₂, LiBF₂(C₂O₄), LiCF₃BF₃, or a combination thereof. The preferred concentration of lithium salt in the electrolyte ranges from 0.5 to 1.5 mol/L.

The organic solvent of the non-aqueous electrolyte is selected from carbonate, carbonate ester (organic carbonate or organocarbonate), carboxylate, carboxylate ester, ethers, ketones or combinations thereof. Among them, carbonates may be any one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), and dipropyl carbonate, Dibutyl carbonate, or a combination thereof. The carboxylic acid esters may be any one of methyl acetate, ethyl acetate, methyl butyrate, ethyl butyrate, methyl propionate, ethyl propionate, propyl acetate, and a combination thereof.

Other organic solvents is suitably selected from one of a cyclic ether such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, a chain ether such as 1,2-dimethoxyethane, 1,2-diethoxy ethane, 1,2-dibutoxyethane, an amide such as dimethylformamide, and a sulfide such as sulfolane, a lactone such as γ-butyrolactone, γ-valerolactone, or the organic solvents may be a combination of two of the above.

In an embodiment of the invention, there is provided a lithium-ion battery which has a positive electrode (cathode), a negative electrode (anode), a separator interposed between the positive and negative electrodes, and an added non-aqueous electrolyte. The positive and negative electrodes contain active materials that permit intercalation and exfoliation of lithium ions. Active material of cathode may be any one or a combination of lithium oxide compounds with metal elements such as vanadium, titanium, chromium, copper, aluminum, iron, nickel, cobalt, manganese, addition of other transition metals or non-transition metal to the aforementioned lithium transition metal oxides compounds, as well as mixture thereof. The specific crystal structure may be a layered lithium containing oxide, a spinel type lithium-containing oxides, or an olivine-type of lithium-containing phosphate compounds, etc. The cathode may contain one of the aforementioned active materials or a combination of two of more of those active materials. Active material of anode may be any one of or a combination of soft carbon, hard carbon, artificial graphite, natural graphite, meso carbon micro bead (MCMB), silicon, silicon oxide compound, silicon carbon composite, lithium titanate oxide, and metals that can form alloys with lithium, etc. Specifically, a carbon-based, silicon-based, tin-based negative electrode can be used. The anode may contain one or more of the aforementioned active materials.

In the above-mentioned lithium-ion battery, the positive and negative electrodes further include a binder and a conductive agent. A slurry of cathode material which contains the cathode active material, a binder and a conductive agent is coated on a current collector of positive electrode. The positive electrode is formed after the slurry dries. Similarly, the slurry of anode material which may include an anode active material, a binder and a conductive agent is coated on the current collector of a negative electrode. The negative electrode is obtained after the slurry dries.

The separator may be formed from any material that is commercially available for making suitable separators in commercial batteries such as but not limited to polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), ceramics materials, glass fibers or composite films of a combination of the above listed.

The electrolyte is the non-aqueous electrolyte as described.

The following embodiments are provided as examples only for explaining the invention.

Embodiment 1

The synthesis of ionic liquid with two-core cationic chain (structural formula I: Z₁X₁YX₂Z₂)

Step 1. Synthesis of Two-Core Cationic Halide

-   -   1. Taking the synthesis of 1,4-bis(1-methylpyrrolidium 1-yl)         butane dichloride (DiPYR₁₄Cl₂) as an example: N-methyl         pyrrolidine (NMPD) is purified by distillation at 85° C., and         then mixed them at the mole ratio of NMPD:1,4-dichlorobutane at         2:1.1, followed by the addition of acetone which is at a volume         same as that of the dichloroalkyl. It is then mixed and stirred         at 70° C. for 16 hours and distilled to remove the acetone. The         resulting liquid is DiPYR₁₄Cl₂.     -   2. Change the alkyl chain Y to other functional groups, such as         sulfonyl, carbonate, ether, ketone, ester, etc. Taking the         synthesis of bis [2-(1-methylpyrrolidinium 1-yl) ethyl] ether         dichloride (DiPYR_(IEE)Cl₂) as an example (No. 8 of FIG. 1         /Table 1): Firstly, N-methyl pyrrolidine (NMPD) is purified by         distillation at 85° C., and then NMPD and bis(2-chloroethyl)         ether are mixed at a mole ratio of 2:1.1 followed by the         addition of acetone which is at a volume same as the         bis(2-chloroethyl) ether. It is then mixed and stirred at 70° C.         for 16 hours and distilled to remove the acetone. The resulting         liquid is DiPYR_(IEE)Cl₂.

The synthesis parameters of other series of bis(1-methylpyrrolidium) alkyl halide ionic liquids are shown in FIG. 1 /Table 1.

With reference to FIG. 1 /Table 1, the synthesis of DiPYR₁₄Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,     -   2) NMPD and 1,4-Dichlorobutane are mixed at a mole ratio of         2:1.1.     -   3) Addition of acetone which is at a volume same as the         1,4-Dichlorobutane.     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Distilled to remove the acetone. The resulting liquid is         DiPYR₁₄Cl₂.

With reference to FIG. 1 /Table 1, the synthesis of DiPYR₁₅Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,     -   2) NMPD and 1,5-Dichloropentane are mixed at a mole ratio of         2:1.1.     -   3) Addition of acetone which is at a volume same as the         1,5-Dichloropentane.     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Distilled to remove the acetone. The resulting liquid is         DiPYR₁₅Cl₂.

With reference to FIG. 1 /Table 1, the synthesis of DiPYR₁₆Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,     -   2) NMPD and 1,6-Dichlorohexane are mixed at a mole ratio of         2:1.1.     -   3) Addition of acetone which is at a volume same as the         1,6-Dichlorohexane.     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Distilled to remove the acetone. The resulting liquid is         DiPYR₁₆Cl₂.

With reference to FIG. 1 /Table 1, the synthesis of DiPYR₁₇Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,     -   2) NMPD and 1,7-Dichloroheptane are mixed at a mole ratio of         2:1.1.     -   3) Addition of acetone which is at a volume same as the         1,7-Dichloroheptane.     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Distilled to remove the acetone. The resulting liquid is         DiPYR₁₇Cl₂.

With reference to FIG. 1 /Table 1, the synthesis of DiPYR₁₈Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,     -   2) NMPD and 1,8-Dichlorooctane are mixed at a mole ratio of         2:1.1.     -   3) Addition of acetone which is at a volume same as the         1,8-Dichlorooctane.     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Distilled to remove the acetone. The resulting liquid is         DiPYR₁₈Cl₂.

With reference to FIG. 1 /Table 1, the synthesis of DiPYR₁₉Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,     -   2) NMPD and 1,9-Dichlorononane are mixed at a mole ratio of         2:1.1.     -   3) Addition of acetone which is at a volume same as the         1,9-Dichlorononane.     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Distilled to remove the acetone. The resulting liquid is         DiPYR₁₉Cl₂.

With reference to FIG. 1 /Table 1, the synthesis of DiPYR₁₁₀Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,     -   2) NMPD and 1,10-Dichlorodecane are mixed at a mole ratio of         2:1.1.     -   3) Addition of acetone which is at a volume same as the         1,10-Dichlorodecane.     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Distilled to remove the acetone. The resulting liquid is         DiPYR₁₁₀Cl₂.

With reference to FIG. 1 /Table 1, the synthesis of DiPYR_(IEE)Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,     -   2) NMPD and Bis(2-chloroethyl)ether are mixed at a mole ratio of         2:1.1.     -   3) Addition of acetone which is at a volume same as the         Bis(2-chloroethyl)ether.     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Distilled to remove the acetone. The resulting liquid is         DiPYR_(IEE)Cl₂.

With reference to FIG. 1 /Table 1, the synthesis of DiPYR_(IEC)Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,     -   2) NMPD and Bis(2-chloroethyl) carbonate are mixed at a mole         ratio of 2:1.1.     -   3) Addition of acetone which is at a volume same as the         Bis(2-chloroethyl) carbonate.     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Distilled to remove the acetone. The resulting liquid is         DiPYR_(IEC)Cl₂.

With reference to FIG. 1 /Table 1, the synthesis of DiPYR_(IPO)Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,     -   2) NMPD and 1,5-dichloro pentan-3-one are mixed at a mole ratio         of 2:1.1.     -   3) Addition of acetone which is at a volume same as the         1,5-dichloro pentan-3-one.     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Distilled to remove the acetone. The resulting liquid is         DiPYR_(IPO)Cl₂.

With reference to FIG. 1 /Table 1, the synthesis of DiPYR_(IEB)Cl₂:

-   -   1) NMPD is purified by distillation at 85° C.,     -   2) NMPD and Bis(2-chloroethyl) butanedioate are mixed at a mole         ratio of 2:1.1.     -   3) Addition of acetone which is at a volume same as the         Bis(2-chloroethyl) butanedioate.     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Distilled to remove the acetone. The resulting liquid is         DiPYR_(IEB)Cl₂.         -   3. Replacing the cations X₁ and X₂ with other heterocyclic             aromatic or amine, which may include imidazolium, quaternary             ammonium, piperidinium, pyrrolidinium, morpholinium,             trimethylamine, etc. Taking the synthesis of             1,5-bis(1-methylpiperidinium 1-yl) pentane dichloride             (DiPIP₁₅Cl₂) as an example: N-methyl piperidine (MPIP) is             purified by vacuum distillation, and then MPIP and             1,5-dichloropentane are mixed at the mole ratio of 2:1.1             followed by the addition of acetone which has a volume same             as that of the dichloroalkyl. It is then mixed and stirred             at 70° C. for 16 hours. After distilling off the acetone,             the remaining liquid is DiPIP₁₅Cl₂.     -   Taking the synthesis of 1,5-(1-methylpyrrolidium         1-yl)(1-methylpiperidinium 1-yl) pentane dichloride         (PYRPIP₁₅Cl₂) as an example (no. 5 of FIG. 2 /Table 2). N-methyl         pyrrolidine (NMPD) and N-methyl piperidine (MPIP) are purified         by vacuum distillation. NMPD, MPIP, and 1,5-Dichloropentane are         mixed at a mole ratio of 1:1:1.1 followed by the addition of         acetone which is in the same volume as the 1,5-Dichloropentane.         It is then mixed and stirred at 70° C. for 16 hours. After the         acetone is distilled off, the remaining liquid is PYRPIP₁₅Cl₂.         The synthesis parameters of other series of two-core cationic         halide ionic liquid are shown in FIG. 2 /Table 2

With reference to FIG. 2 /Table 2, the synthesis of DiPYR₁₅Cl₂:

-   -   1) N-methyl pyrrolidine (NMPD) is purified by distillation at         85° C.     -   2) NMPD and 1,5-Dichloropentane are mixed at a mole ratio of         2:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Acetone is distilled off and the remaining liquid is         DiPYR₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of DiPIP₁₅Cl₂:

-   -   1) N-methyl piperidine (MPIP) is purified by vacuum         distillation.     -   2) MPIP and 1,5-Dichloropentane are mixed at a mole ratio of         2:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Acetone is distilled off and the remaining liquid is         DiPIP₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of DiTEA₁₅Cl₂:

-   -   1) Triethylamine (TEA) is purified by vacuum distillation.     -   2) TEA and 1,5-Dichloropentane are mixed at a mole ratio of         2:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Acetone is distilled off and the remaining liquid is         DiTEA₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of DiMIM₁₅Cl₂:

-   -   1) 1-methylimidazole (MIM) is purified by vacuum distillation.     -   2) MIM and 1,5-Dichloropentane are mixed at a mole ratio of         2:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 25° C. for 12 hours.     -   5) Acetone is distilled off and the remaining liquid is         DiMIM₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of PYRPIP₁₅Cl₂:

-   -   1) NMPD and MPIP are purified by vacuum distillation.     -   2) NMPD and MPIP and 1,5-Dichloropentane are mixed at a mole         ratio of 1:1:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Acetone is distilled off and the remaining liquid is         PYRPIP₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of PYRTEA₁₅Cl₂:

-   -   1) NMPD and TEA are purified by vacuum distillation.     -   2) NMPD and TEA and 1,5-Dichloropentane are mixed at a mole         ratio of 1:1:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Acetone is distilled off and the remaining liquid is         PYRTEA₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of PYRMPE₁₅Cl₂:

-   -   1) NMPD and Morpholine (MPE) are purified by vacuum         distillation.     -   2) NMPD and MPE and 1,5-Dichloropentane are mixed at a mole         ratio of 1:1:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 45° C. for 12 hours.     -   5) Acetone is distilled off and the remaining liquid is         PYRMPE₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of PYRMIM₁₅Cl₂:

-   -   1) NMPD and MIM are purified by vacuum distillation.     -   2) NMPD and MIM and 1,5-Dichloropentane are mixed at a mole         ratio of 1:1:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 25° C. for 12 hours.     -   5) Acetone is distilled off and the remaining liquid is         PYRMPE₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of PYRPYO₁₅Cl₂:

-   -   1) NMPD and Pyrrole (PYO) are purified by vacuum distillation.     -   2) NMPD and PYO and 1,5-Dichloropentane are mixed at a mole         ratio of 1:1:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 45° C. for 12 hours.     -   5) Acetone is distilled off and the remaining liquid is         PYRPYO₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of PIPTEA₁₅Cl₂:

-   -   1) MPIP and TEA are purified by vacuum distillation.     -   2) MPIP and TEA and 1,5-Dichloropentane are mixed at a mole         ratio of 1:1:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 70° C. for 16 hours.     -   5) Acetone is distilled off and the remaining liquid is         PIPTEA₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of PIPMPE₁₅Cl₂:

-   -   1) MPIP and MPE are purified by vacuum distillation.     -   2) MPIP and MPE and 1,5-Dichloropentane are mixed at a mole         ratio of 1:1:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 45° C. for 12 hours.     -   5) Acetone is distilled off and the remaining liquid is         PIPMPE₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of PIPMIM₁₅Cl₂:

-   -   1) MPIP and MIM are purified by vacuum distillation.     -   2) MPIP and MIM and 1,5-Dichloropentane are mixed at a mole         ratio of 1:1:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 25° C. for 12 hours.     -   5) Acetone is distilled off and the remaining liquid is         PIPMIM₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of PIPPYO₁₅Cl₂:

-   -   1) MPIP and PYO are purified by vacuum distillation.     -   2) MPIP and PYO and 1,5-Dichloropentane are mixed at a mole         ratio of 1:1:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 45° C. for 12 hours.     -   5) Acetone is distilled off and the remaining liquid is         PIPPYO₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of TEAMPE₁₅Cl₂:

-   -   1) TEA and MPE are purified by vacuum distillation.     -   2) TEA and MPE and 1,5-Dichloropentane are mixed at a mole ratio         of 1:1:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 45° C. for 12 hours.     -   5) Acetone is distilled off and the remaining liquid is         TEAMPE₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of TEAMIM₁₅Cl₂:

-   -   1) TEA and MIM are purified by vacuum distillation.     -   2) TEA and MIM and 1,5-Dichloropentane are mixed at a mole ratio         of 1:1:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 25° C. for 12 hours.     -   5) Acetone is distilled off and the remaining liquid is         TEAMIM₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of TEAPYO₁₅Cl₂:

-   -   1) TEA and PYO are purified by vacuum distillation.     -   2) TEA and PYO and 1,5-Dichloropentane are mixed at a mole ratio         of 1:1:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 45° C. for 12 hours.     -   5) Acetone is distilled off and the remaining liquid is         TEAPYO₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of MIMMPE₁₅Cl₂:

-   -   1) MIM and MPE are purified by vacuum distillation.     -   2) MIM and MPE and 1,5-Dichloropentane are mixed at a mole ratio         of 1:1:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 25° C. for 12 hours.     -   5) Acetone is distilled off and the remaining liquid is         MIMMPE₁₅Cl₂.

With reference to FIG. 2 /Table 2, the synthesis of MIMPYO₁₅Cl₂:

-   -   1) MIM and PYO are purified by vacuum distillation.     -   2) MIM and PYO and 1,5-Dichloropentane are mixed at a mole ratio         of 1:1:1.1     -   3) Adding acetone which is in the same volume as the         1,5-Dichloropentane     -   4) Mix and stir at 25° C. for 12 hours.     -   5) Acetone is distilled off and the remaining liquid is         MIMPYO₁₅Cl₂.

Step 2. Synthesis of Two-Core Cationic Chain Ionic Liquid

-   1. Taking the synthesis of 1,4-bis(1-methylpyrrolidium 1-yl) butane     dihexafluorophosphate [DiPYR₁₄(PF₆)₂] as an example:     1,4-bis(1-methylpyrrolidium 1-yl) butane dichloride (DiPYR₁₄Cl₂)     synthesized in Step 1 is added to an equal weight of acetone (as a     mixed solvent). followed by adding twice as many mole of potassium     hexafluorophosphate. It is stirred at 70° C. for 16 hours. After     filtering the white precipitate potassium chloride KCl, the     remaining liquid is distilled under reduced pressure to remove the     acetone, and then recrystallized to form DiPYR₁₄(PF₆)₂. Finally, the     synthesized product is filtered, purified and dried in a vacuum oven     at 60° C. until its water content is less than 20 ppm. The synthesis     parameters of other series of DiPYR_(1R)(PF₆)₂ and DiPIP_(1R)(PF₆)₂     ionic liquids are shown in FIG. 3A or Table 3.     -   With reference to FIG. 3A/Table 3, the synthesis of         DiPYR₁₄(PF₆)₂:     -   1) DiPYR₁₄Cl₂ synthesized in Step 1 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPYR₁₄(PF₆)₂     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         DiPYR₁₅(PF₆)₂:     -   1) DiPYR₁₅Cl₂ synthesized in Step 1 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPYR₁₅(PF₆)₂.     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         DiPYR₁₆(PF₆)₂:     -   1) DiPYR₁₆Cl₂ synthesized in Step 1 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPYR₁₆(PF₆)₂     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         DiPYR₁₈(PF₆)₂:     -   1) DiPYR₁₈Cl₂ synthesized in Step 1 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPYR₁₈(PF₆)₂.     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         DiPIP₁₄(PF₆)₂:     -   1) DiPIP₁₄(PF₆)₂ synthesized in Step 2 is added to an equal         weight of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPIP₁₄(PF₆)₂     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         DiPIP₁₅(PF₆)₂:     -   1) DiPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPIP₁₅(PF₆)₂.     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         DiPIP₁₆(PF₆)₂:     -   1) DiPIP₁₆Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPIP₁₆(PF₆)₂.     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         DiPIP₁₈(PF₆)₂:     -   1) DiPIP₁₈Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPIP₁₈(PF₆)₂.     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm. -   2. Replacing the cation X₁ and X₂ with other heterocyclic aromatics     or amine, including imidazolium, quaternary ammonium, piperidinium,     pyrrolidinium, morpholinium, and triethylamine etc. Taking the     synthesis of 1,5-(1-methylpyrrolidium 1-yl)(1-methyl piperidinium     1-yl) pentane dihexafluorophosphate [PYRPIP₁₅(PF₆)₂] as an example:     The 1,5-(1-methylpyrrolidium 1-yl)(1-methylpiperidinium 1-yl)     pentane dichloride (PYRPIP₁₅Cl₂) synthesized in Step 1 is added to     an equal weight of acetone (as a mixed solvent). Twice the mole of     potassium hexafluorophosphate is then added. It is stirred at 70° C.     for 16 hours. After the white precipitate potassium chloride KCl is     filtered, the remaining liquid is distilled under reduced pressure     to remove the acetone, and then recrystallized to form     PYRPIP₁₅(PF₆)₂. Finally, the synthesized product is filtered and     purified and dried in a vacuum oven at 60° C. until its water     content is less than 20 ppm. The synthesis parameters of other     series of two-core cationic chain ionic liquids are shown in FIGS.     3A, 3B or Table 3.     -   With reference to FIG. 3A/Table 3, the synthesis of         PYRPIP₁₅(PF₆)₂:     -   1) PYRPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PYRPIP₁₅(PF₆)₂     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         PYRTEA₁₅(PF₆)₂:     -   1) PYRTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PYRTEA₁₅(PF₆)₂     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         PYRMPE₁₅(PF₆)₂:     -   1) PYRMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 45° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PYRMPE₁₅(PF₆)₂     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         PYRMIM₁₅(PF₆)₂:     -   1) PYRMIM₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 25° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PYRMIM₁₅(PF₆)₂     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         PYRPYO₁₅(PF₆)₂:     -   1) PYRPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 45° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PYRPYO₁₅(PF₆)₂     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         PIPTEA₁₅(PF₆)₂:     -   1) PIPTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PIPTEA₁₅(PF₆)₂     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         PIPMPE₁₅(PF₆)₂:     -   1) PIPMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 45° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PIPMPE₁₅(PF₆)₂     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         PIPMIM₁₅(PF₆)₂:     -   1) PIPMIM₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 25° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PIPMIM₁₅(PF₆)₂.     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         PIPPYO₁₅(PF₆)₂:     -   1) PIPPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 45° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PIPPYO₁₅(PF₆)₂.     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         TEAMPE₁₅(PF₆)₂:     -   1) TEAMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 45° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form TEAMPE₁₅(PF₆)₂.     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of         TEAMIM₁₅(PF₆)₂:     -   1) TEAMIM₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 25° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form TEAMIM₁₅(PF₆)₂.     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         TEAPYO₁₅(PF₆)₂:     -   1) TEAPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 45° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form TEAPYO₁₅(PF₆)₂     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         MIMMPE₁₅(PF₆)₂:     -   1) MIMMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 25° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form MIMMPE₁₅(PF₆)₂     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         MIMPYO₁₅(PF₆)₂:     -   1) MIMPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding twice as many moles of potassium hexafluorophosphate.     -   3) Stir at 25° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form MIMPYO₁₅(PF₆)₂     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm. -   3. Replacing the other anion Z₁ and Z₂, which may include PF₆ ⁻     (hexafluorophosphate), POF₂ ⁻ (difluorophosphate), BF₄ ⁻     (tetrafluoroborate), B(C₂O₄)₂ ⁻ (BOB⁻, bis(oxalato) borate),     BF₂(C₂O₄)⁻ (ODFB⁻, difluoro(oxalato)borate), CF₃BF₃ ⁻     (trifluoromethyltrifluoroborate), (FSO₂)₂N⁻ (FSI⁻,     bis(fluorosulfonyl)imide), (CF₃SO₂)₂N (TFSI⁻,     bis(trifluoromethane)sulfonamide), CH₃SO₄ ⁻ (MeSO₄ ⁻, methyl     sulfate), etc.     -   Taking the synthesis of 1,5-(1-methylpyrrolidium         1-yl)(1-methylpiperidinium) 1-yl) pentane hexafluorophosphate         tetrafluoroborate [PYRPIP₁₅(PF₆)(BF₄)] as an example. The         1,5-(1-methylpyrrolidium 1-yl)(1-methylpiperidinium 1-yl)         pentane dichloride (PYRPIP₁₅Cl₂) synthesized in Step 1 is added         to an equal weight of acetone (as a mixed solvent) followed by         the addition of same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate. It is stirred at 70° C. for 16         hours. After the white precipitate potassium chloride KCl is         filtered, the remaining liquid is distilled under reduced         pressure to remove the acetone, and then recrystallized to form         PYRPIP₁₅(PF₆)(BF₄). Finally, the synthesized product is         filtered, purified, and dried in a vacuum oven at 60° C. to         until its water content is below 20 ppm. The synthesis         parameters of other series of two-core cationic chain ionic         liquids are shown in FIGS. 3A/3B/Table 3.     -   With reference to FIG. 3A/Table 3, the synthesis of DiPYR₁₄(PF₆)         (BF₄):     -   1) DiPYR₁₄Cl₂ synthesized in Step 1 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPYR₁₄(PF₆) (BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of DiPYR₁₅(PF₆)         (BF₄):     -   1) DiPYR₁₅Cl₂ synthesized in Step 1 is added to an equal weight         of acetone     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPYR₁₅(PF₆) (BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of DiPYR₁₆(PF₆)         (BF₄):     -   1) DiPYR₁₆Cl₂ synthesized in Step 1 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPYR₁₆(PF₆) (BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of DiPYR₁₈(PF₆)         (BF₄):     -   1) DiPYR₁₈Cl₂ synthesized in Step 1 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPYR₁₈(PF₆) (BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of DiPIP₁₄(PF₆)         (BF₄):     -   1) DiPIP₁₄Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPIP₁₄(PF₆) (BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 3A/Table 3, the synthesis of DiPIP₁₅(PF₆) (BF₄):

-   -   1) DiPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPIP₁₅(PF₆) (BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of DiPIP₁₆(PF₆)         (BF₄):     -   1) DiPIP₁₆Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPIP₁₆(PF₆) (BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3A/Table 3, the synthesis of DiPIP₁₈(PF₆)         (BF₄):     -   1) DiPIP₁₈Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPIP₁₈(PF₆) (BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         PYRPIP₁₅(PF₆)(BF₄):     -   1) PYRPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PYRPIP₁₅(PF₆)(BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         PYRTEA₁₅(PF₆)(BF₄):     -   1) PYRTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PYRTEA₁₅(PF₆)(BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         PYRMPE₁₅(PF₆)(BF₄):     -   1) PYRMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 45° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PYRMPE₁₅(PF₆)(BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         PYRMIM₁₅(PF₆)(BF₄):     -   1) PYRMIM₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 25° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PYRMIM₁₅(PF₆)(BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         PYRPYO₁₅(PF₆)(BF₄):     -   1) PYRPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 45° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PYRPYO₁₅(PF₆)(BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         PIPTEA₁₅(PF₆)(BF₄):     -   1) PIPTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PIPTEA₁₅(PF₆)(BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         PIPMPE₁₅(PF₆)(BF₄):     -   1) PIPMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 45° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PIPMPE₁₅(PF₆)(BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         PIPMIM₁₅(PF₆)(BF₄):     -   1) PIPMIM₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 25° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PIPMIM₁₅(PF₆)(BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         PIPPYO₁₅(PF₆)(BF₄):     -   1) PIPPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 45° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PIPPYO₁₅(PF₆)(BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         TEAMPE₁₅(PF₆)(BF₄):     -   1) TEAMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 45° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form TEAMPE₁₅(PF₆)(BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         TEAMIM₁₅(PF₆)(BF₄):     -   1) TEAMIM₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 25° C. for 12 hours     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form TEAMIM₁₅(PF₆)(BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         TEAPYO₁₅(PF₆)(BF₄):     -   1) TEAPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 45° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form TEAPYO₁₅(PF₆)(BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         MIMMPE₁₅(PF₆)(BF₄):     -   1) MIMMPE₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 25° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form MIMMPE₁₅(PF₆)(BF₄):     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         MIMPYO₁₅(PF₆)(BF₄):     -   1) MIMPYO₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of potassium hexafluorophosphate and         potassium tetrafluoroborate.     -   3) Stir at 25° C. for 12 hours.     -   4) Filtering the white precipitate KCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form MIMPYO₁₅(PF₆)(BF₄).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         DiPYR₁₅(TFSI)(FSI):     -   1) DiPYR₁₅Cl₂ synthesized in Step 1 is added to an equal weight         of acetone.     -   2) Adding same mole of lithium trifluoromethanesulfonimide and         lithium bis(fluorosulfonyl)imide.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate LiCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPYR₁₅(TFSI)(FSI).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         DiPIP₁₅(TFSI)(FSI):     -   1) DiPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of lithium bis(trifluoromethane)sulfonimide         and lithium bis(fluorosulfonyl)imide.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate LiCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPIP₁₅(TFSI)(FSI).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         PYRPIP₁₅(TFSI)(FSI):     -   1) PYRPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of lithium bis(trifluoromethane)sulfonimide         and lithium bis(fluorosulfonyl)imide.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate LiCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PYRPIP₁₅(TFSI)(FSI).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         PYRTEA₁₅(TFSI)(FSI):     -   1) PYRTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of lithium bis(trifluoromethane)sulfonimide         and lithium bis(fluorosulfonyl)imide.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate LiCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PYRTEA₁₅(TFSI)(FSI).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         PIPTEA₁₅(TFSI)(FSI):     -   1) PIPTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of lithium bis(trifluoromethane)sulfonimide         and lithium bis(fluorosulfonyl)imide     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate LiCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PIPTEA₁₅(TFSI)(FSI).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         DiPYR₁₅(CF₃BF₃)(POF₂):     -   1) DiPYR₁₅Cl₂ synthesized in Step 1 is added to an equal weight         of acetone.     -   2) Adding same mole of lithium (trifluoromethyl)trifluoroborate         and lithium difluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate LiCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPYR₁₅(CF₃BF₃)(POF₂).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         DiPIP₁₅(CF₃BF₃)(POF₂):     -   1) DiPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of lithium (trifluoromethyl)trifluoroborate         and lithium difluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate LiCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form DiPIP₁₅(CF₃BF₃)(POF₂).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         PYRPIP₁₅(CF₃BF₃)(POF₂):     -   1) PYRPIP₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of lithium (trifluoromethyl)trifluoroborate         and lithium difluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate LiCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PYRPIP₁₅(CF₃BF₃)(POF₂).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         PYRTEA₁₅(CF₃BF₃)(POF₂):     -   1) PYRTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of lithium (trifluoromethyl)trifluoroborate         and lithium difluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate LiCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PYRTEA₁₅(CF₃BF₃)(POF₂).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.     -   With reference to FIG. 3B/Table 3, the synthesis of         PIPTEA₁₅(CF₃BF₃)(POF₂):     -   1) PIPTEA₁₅Cl₂ synthesized in Step 2 is added to an equal weight         of acetone.     -   2) Adding same mole of lithium (trifluoromethyl)trifluoroborate         and lithium difluorophosphate.     -   3) Stir at 70° C. for 16 hours.     -   4) Filtering the white precipitate LiCl.     -   5) Distill the remaining liquid under reduced pressure to remove         the acetone.     -   6) Recrystallize to form PIPTEA₁₅(CF₃BF₃)(POF₂).     -   7) The product is filtered, purified and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

Embodiment 2

Synthesis of Ionic Liquid with the Aromatic Functional Group Bonded to a Cation (Structural Formula II: Z₁X₁YW)

Step 1. Synthesis of Aromatic Group Bonded to Cation Halide

-   1. Taking the synthesis of benzyl-2-(1-methylpyrrolidinium 1-yl)     ethyl ether chloride (Benzyl-PYR_(IEE)Cl) as an example. Firstly,     N-methyl pyrrolidine (NMPD) is purified by distillation at 85° C.     Then NMPD and Benzyl 2-chloroethyl ether are mixed at the mole ratio     of 1:1.1 followed by adding acetone of the same volume as the     benzyl-2-chloroethyl ether. It is mixed and stirred at 70° C. for 12     hours. Acetone is distilled off with the remaining liquid being     benzyl-PYR_(IEE)Cl. The synthesis parameters of other series of     aromatic bonded to 1-methylpyrrolidinium halide are shown in FIG. 4     /Table 4. -   2. The synthesis of 1-(2-Furoyl)-1-methyl pyrrolidinium chloride     (Furoyl-PYR₁₁Cl) as an example. First, N-methyl pyrrolidine (NMPD)     is purified by distillation at 85° C. Then NMPD and 2-Furoyl     chloride are mixed at a mole ratio of 1:1.1 followed by adding     acetone at the same volume as the 2-furoyl chloride. It is then     mixed and stirred at 70° C. for 12 hours. Acetone is removed by     distillation and the remaining liquid is Furoyl-PYR₁₁Cl. The     synthesis parameters of other series of aromatic bonded to     1-methylpyrrolidinium halide are shown in FIG. 4 /Table 4.     -   With reference to FIG. 4 /Table 4, the synthesis of         Benzyl-PYR_(IEE)Cl:     -   1) NMPD is purified by distillation at 85° C.     -   2) NMPD and Benzyl-2-chloroethyl ether are mixed at the mole         ratio of 1:1.1.     -   3) Adding acetone of the same volume as the Benzyl-2-chloroethyl         ether.     -   4) Mix and stir at 70° C. for 12 hours.     -   5) Acetone is distilled off with the remaining liquid being         Benzyl-PYR_(IEE)Cl.     -   With reference to FIG. 4 /Table 4, the synthesis of         Benzyl-PYR_(IBE)Cl:         -   1) NMPD is purified by distillation at 85° C.         -   2) NMPD and Benzyl-4-chloro butyl ether are mixed at the             mole ratio of 1:1.1.         -   3) Adding acetone of the same volume as the Benzyl-4-chloro             butyl ether.         -   4) Mix and stir at 70° C. for 12 hours.         -   5) Acetone is distilled off with the remaining liquid being             Benzyl-PYR_(IBE)Cl.     -   With reference to FIG. 4 /Table 4, the synthesis of         Benzoyl-PYR₁₁Cl:         -   1) NMPD is purified by distillation at 85° C.         -   2) NMPD and Benzoyl chloride are mixed at the mole ratio of             1:1.1.         -   3) Adding acetone of the same volume as the Benzoyl             chloride.         -   4) Mix and stir at 70° C. for 12 hours.         -   5) Acetone is distilled off with the remaining liquid being             Benzoyl-PYR₁₁Cl.     -   With reference to FIG. 4 /Table 4, the synthesis of         Phenacyl-PYR₁₁Cl:         -   1) NMPD is purified by distillation at 85° C.         -   2) NMPD and Phenacyl chloride are mixed at the mole ratio of             1:1.1.         -   3) Adding acetone of the same volume as the Phenacyl             chloride.         -   4) Mix and stir at 70° C. for 12 hours.         -   5) Acetone is distilled off with the remaining liquid being             Phenacyl-PYR₁₁Cl.     -   With reference to FIG. 4 /Table 4, the synthesis of         Furan-PYR₁₁Cl:         -   1) NMPD is purified by distillation at 85° C.         -   2) NMPD and 2-Chlorofuran are mixed at the mole ratio of             1:1.1.         -   3) Adding acetone of the same volume as the 2-Chlorofuran.         -   4) Mix and stir at 70° C. for 12 hours.         -   5) Acetone is distilled off with the remaining liquid being             Furan-PYR₁₁Cl.     -   With reference to FIG. 4 /Table 4, the synthesis of         Furan-PYR₁₄Cl:         -   1) NMPD is purified by distillation at 85° C.         -   2) NMPD and 2-(4-chlorobutyl)furan are mixed at the mole             ratio of 1:1.1.         -   3) Adding acetone of the same volume as the             2-(4-chlorobutyl)furan.         -   4) Mix and stir at 70° C. for 12 hours.         -   5) Acetone is distilled off with the remaining liquid being             Furan-PYR₁₄Cl.     -   With reference to FIG. 4 /Table 4, the synthesis of         Furoyl-PYR₁₁Cl:         -   1) NMPD is purified by distillation at 85° C.         -   2) NMPD and 2-Furoyl chloride are mixed at the mole ratio of             1:1.1.         -   3) Adding acetone of the same volume as the 2-Furoyl             chloride.         -   4) Mix and stir at 70° C. for 12 hours.         -   5) Acetone is distilled off with the remaining liquid being             Furoyl-PYR₁₁Cl.     -   With reference to FIG. 4 /Table 4, the synthesis of         Benzenesulfonyl-PYR₁₁Cl:         -   1) NMPD is purified by distillation at 85° C.         -   2) NMPD and Benzenesulfonyl chloride are mixed at the mole             ratio of 1:1.1.         -   3) Adding acetone of the same volume as the Benzenesulfonyl             chloride.         -   4) Mix and stir at 70° C. for 12 hours.         -   5) Acetone is distilled off with the remaining liquid being             Benzenesulfonyl-PYR₁₁Cl.     -   With reference to FIG. 4 /Table 4, the synthesis of         p-Toluenesulfonyl-PYR₁₁Cl:         -   1) NMPD is purified by distillation at 85° C.         -   2) NMPD and p-Toluenesulfonyl chloride are mixed at the mole             ratio of 1:1.1.         -   3) Adding acetone of the same volume as the             p-Toluenesulfonyl chloride.         -   4) Mix and stir at 70° C. for 12 hours.         -   5) Acetone is distilled off with the remaining liquid being             p-Toluenesulfonyl-PYR₁₁Cl. -   3. Replacing the cation X₁ with other heterocyclic aromatic or amine     such as imidazolium, quaternary ammonium, piperidinium,     pyrrolidinium, morpholinium, triethylamine etc. Taking the synthesis     of 1-(2-Furoyl)-1-methyl piperidinium chloride (Furoyl-PIP₁₁Cl) as     an example. Firstly, N-methyl piperidine (MPIP) is purified by     vacuum distillation, and then the MPIP and 2-Furoyl chloride are     mixed at a mole ratio of 1:1.1. Acetone, same volume as 2-furoyl     chloride, is added. It is mixed and stirred at 70° C. for 12 hours.     Acetone is distilled off with the remaining liquid as     Furoyl-PIP₁₁Cl. The synthesis parameters of other series of aromatic     bonded to cation halide ionic liquids are shown in FIG. 5 /Table 5.

With reference to FIG. 5 /Table 5, the synthesis of Benzyl-PYR_(IEE)Cl:

-   -   1) NMPD is purified by distillation at 85° C.     -   2) NMPD and Benzyl 2-chloroethyl ether are mixed at a mole ratio         of 1:1.1.     -   3) Acetone, same volume as Benzyl 2-chloroethyl ether, is added.     -   4) Mix and stir at 70° C. for 12 hours.     -   5) Acetone is distilled off with the remaining liquid as         Benzyl-PYR_(IEE)Cl.

With reference to FIG. 5 /Table 5, the synthesis of Furan-PYR₁₄Cl:

-   -   1) NMPD is purified by distillation at 85° C.     -   2) NMPD and 2-(4-chlorobutyl)furan are mixed at a mole ratio of         1:1.1.     -   3) Acetone, same volume as 2-(4-chlorobutyl)furan, is added.     -   4) Mix and stir at 70° C. for 12 hours.     -   5) Acetone is distilled off with the remaining liquid as         Furan-PYR₁₄Cl.

With reference to FIG. 5 /Table 5, the synthesis of Furoyl-PYR₁₁Cl:

-   -   1) NMPD is purified by distillation at 85° C.     -   2) NMPD and 2-Furoyl chloride are mixed at a mole ratio of         1:1.1.     -   3) Acetone, same volume as 2-Furoyl chloride, is added.     -   4) Mix and stir at 70° C. for 12 hours.     -   5) Acetone is distilled off with the remaining liquid as         Furoyl-PYR₁₁Cl.

With reference to FIG. 5 /Table 5, the synthesis of Benzyl-PIP_(IEE)Cl:

-   -   1) MPIP is purified by vacuum distillation.     -   2) MPIP and Benzyl 2-chloroethyl ether are mixed at a mole ratio         of 1:1.1.     -   3) Acetone, same volume as Benzyl 2-chloroethyl ether, is added.     -   4) Mix and stir at 70° C. for 12 hours.     -   5) Acetone is distilled off with the remaining liquid as         Benzyl-PIP_(IEE)Cl.

With reference to FIG. 5 /Table 5, the synthesis of Furan-PIP₁₄Cl:

-   -   1) MPIP is purified by vacuum distillation.     -   2) MPIP and 2-(4-chlorobutyl)furan are mixed at a mole ratio of         1:1.1.     -   3) Acetone, same volume as 2-(4-chlorobutyl)furan, is added.     -   4) Mix and stir at 70° C. for 12 hours.     -   5) Acetone is distilled off with the remaining liquid as         Furan-PIP₁₄Cl.

With reference to FIG. 5 /Table 5, the synthesis of Furoyl-PIP₁₁Cl:

-   -   1) MPIP is purified by vacuum distillation.     -   2) MPIP and 2-Furoyl chloride are mixed at a mole ratio of         1:1.1.     -   3) Acetone, same volume as 2-Furoyl chloride, is added.     -   4) Mix and stir at 70° C. for 12 hours.     -   5) Acetone is distilled off with the remaining liquid as         Furoyl-PIP₁₁Cl.

With reference to FIG. 5 /Table 5, the synthesis of Benzyl-TEA_(IEE)Cl:

-   -   1) TEA is purified by vacuum distillation.     -   2) TEA and Benzyl 2-chloroethyl ether are mixed at a mole ratio         of 1:1.1.     -   3) Acetone, same volume as Benzyl 2-chloroethyl ether, is added.     -   4) Mix and stir at 70° C. for 12 hours.     -   5) Acetone is distilled off with the remaining liquid as         Benzyl-TEA_(IEE)Cl.

With reference to FIG. 5 /Table 5, the synthesis of Furan-TEA₁₄Cl:

-   -   1) TEA is purified by vacuum distillation.     -   2) TEA and 2-(4-chlorobutyl)furan are mixed at a mole ratio of         1:1.1.     -   3) Acetone, same volume as 2-(4-chlorobutyl)furan, is added.     -   4) Mix and stir at 70° C. for 12 hours.     -   5) Acetone is distilled off with the remaining liquid as         Furan-TEA₁₄Cl.

With reference to FIG. 5 /Table 5, the synthesis of Furoyl-TEA₁₁Cl:

-   -   1) TEA is purified by vacuum distillation.     -   2) TEA and 2-Furoyl chloride are mixed at a mole ratio of 1:1.1.     -   3) Acetone, same volume as 2-Furoyl chloride, is added.     -   4) Mix and stir at 70° C. for 12 hours.     -   5) Acetone is distilled off with the remaining liquid as         Furoyl-PIP₁₁Cl.

With reference to FIG. 5 /Table 5, the synthesis of Benzyl-MIM_(IEE)Cl:

-   -   1) MIM is purified by vacuum distillation.     -   2) MIM and Benzyl 2-chloroethyl ether are mixed at a mole ratio         of 1:1.1.     -   3) Acetone, same volume as Benzyl 2-chloroethyl ether, is added.     -   4) Mix and stir at 25° C. for 12 hours.     -   5) Acetone is distilled off with the remaining liquid as         Benzyl-PYR_(IEE)Cl.

With reference to FIG. 5 /Table 5, the synthesis of Furan-MIM₁₄Cl:

-   -   1) MIM is purified by vacuum distillation.     -   2) MIM and 2-(4-chlorobutyl)furan mixed at a mole ratio of         1:1.1.     -   3) Acetone, same volume as 2-(4-chlorobutyl)furan, is added.     -   4) Mix and stir at 25° C. for 12 hours.     -   5) Acetone is distilled off with the remaining liquid as         Furan-MIM₁₄Cl.

With reference to FIG. 5 /Table 5, the synthesis of Furoyl-MIM₁₁Cl:

-   -   1) MIM is purified by vacuum distillation.     -   2) MIM and 2-Furoyl chloride are mixed at a mole ratio of 1:1.1.     -   3) Acetone, same volume as 2-Furoyl chloride, is added.     -   4) Mix and stir at 25° C. for 12 hours.     -   5) Acetone is distilled off with the remaining liquid as         Furoyl-MIM₁₁Cl.

With reference to FIG. 5 /Table 5, the synthesis of Furoyl-MPE₁₁Cl:

-   -   1) MPE is purified by vacuum distillation.     -   2) MPE and 2-Furoyl chloride are mixed at a mole ratio of 1:1.1.     -   3) Acetone, same volume as 2-Furoyl chloride, is added.     -   4) Mix and stir at 45° C. for 12 hours.     -   5) Acetone is distilled off with the remaining liquid as         Furoyl-MPE₁₁Cl.

With reference to FIG. 5 /Table 5, the synthesis of Furoyl-PYO₁₁Cl:

-   -   1) PYO is purified by vacuum distillation.     -   2) PYO and 2-Furoyl chloride are mixed at a mole ratio of 1:1.1.     -   3) Acetone, same volume as 2-Furoyl chloride, is added.     -   4) Mix and stir at 45° C. for 12 hours.     -   5) Acetone is distilled off with the remaining liquid as         Furoyl-PYO₁₁Cl.

Step 2. Synthesis of Ionic Liquid with Aromatic Group Bonded to Cation

-   1. Taking the synthesis of 1-(2-Furoyl)-1-methyl pyrrolidinium     hexafluorophosphate (Furoyl-PYR₁₁PF₆) as an example.     1-(2-furoyl)-1-methyl pyrrolidinium chloride (Furoyl-PYR₁₁Cl)     synthesized in Step 1 is added to an equal weight of acetone (as a     mixed solvent) followed by adding a same mole number of potassium     hexafluorophosphate. It is stirred at 70° C. for 12 hours. After the     white precipitate potassium chloride KCl is filtered, the remaining     liquid is distilled under reduced pressure to remove the acetone,     and then recrystallized to form Furoyl-PYR₁₁PF₆. Finally, the     synthesized product is filtered, purified, and dried in a vacuum     oven at 60° C. until its water content is less than 20 ppm. The     synthesis parameters of other series of aromatic bonded to cation     ionic liquid are shown in FIG. 6A, FIG. 6B or Table 6. -   2. Replacing the cation X₁ with other heterocyclic aromatic or     amine, such as imidazolium, quaternary ammonium, piperidinium,     pyrrolidinium, morpholinium, triethylamine etc. Taking the synthesis     of 1-(2-Furoyl)-1-methyl piperidinium hexafluorophosphate     (Furoyl-PIP₁₁PF₆) as an example. 1-(2-furoyl)-1-methyl piperidinium     chloride (Furoyl-PIP₁₁Cl) synthesized in Step 1 is added to an equal     weight of acetone (as a mixed solvent) followed by the same mole     number of potassium hexafluorophosphate. It is stirred at 70° C. for     12 hours. The white precipitate potassium chloride KCl is filtered     out. The remaining liquid is distilled under reduced pressure to     remove acetone, and then recrystallized to form Furoyl-PIP₁₁PF₆.     Finally, the synthesized product is filtered, purified and dried in     a vacuum oven at 60° C. until a water content of less than 20 ppm.     The synthesis parameters of other series of aromatic bonded to     cation ionic liquid are shown in FIG. 6A, FIG. 6B or Table 6. -   3. Replacing anion Z₁ such as PF₆ ⁻ (hexafluorophosphate), POF₂ ⁻     (difluorophosphate), BF₄ ⁻ (tetrafluoroborate), B(C₂O₄)₂ ⁻ (BOB⁻,     bis(oxalato) borate), BF₂(C₂O₄)⁻ (ODFB⁻, difluoro(oxalato)borate),     CF₃BF₃ ⁻(trifluoromethyltrifluoroborate), (FSO₂)₂N⁻ (FSI⁻,     bis(fluorosulfonyl)imide), (CF₃SO₂)₂N⁻ (TFSI⁻,     bis(trifluoromethane)sulfonamide), CH₃SO₄ ⁻ (MeSO₄ ⁻, methyl     sulfate), etc. Taking the synthesis of 1-(2-Furoyl)-1-methyl     pyrrolidinium tetrafluoroborate (Furoyl-PYR₁₁BF₄) as an example.     1-(2-furoyl)-1-methyl pyrrolidinium chloride (Furoyl-PYR₁₁Cl)     synthesized in Step 1 is added to the same weight of acetone (as a     mixed solvent). The same mole number of potassium tetrafluoroborate     is added. It is stirred at 70° C. for 12 hours. The white     precipitate potassium chloride KCl is filtered. The remaining liquid     is distilled under reduced pressure to remove acetone, and then     recrystallized to form Furoyl-PYR₁₁BF₄. Finally, the synthesized     product is filtered purified and dried in a vacuum oven at 60° C.     until its water content is below 20 ppm. The synthesis parameters of     other series of aromatic bonded to cation ionic liquid are shown in     FIG. 6 /Table 6.

With reference to FIG. 6A/Table 6, the synthesis of Benzyl-PYR_(IEE)PF₆:

-   -   1) Benzyl-PYR_(IEE)Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Benzyl-PYR_(IEE)PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A or Table 6, the synthesis of Benzyl-PYR_(IBE)PF₆:

-   -   1) Benzyl-PYR_(IBE)Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Benzyl-PYR_(IBE)PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A or Table 6, the synthesis of Benzoyl-PYR₁₁PF₆:

-   -   1) Benzoyl-PYR₁₁Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Benzoyl-PYR₁₁PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A or table 6, the synthesis of Phenacyl-PYR₁₁PF₆:

-   -   1) Phenacyl-PYR₁₁ in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Phenacyl-PYR₁₁PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furan-PYR₁₁PF₆:

-   -   1) Furan-PYR₁₁Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Furan-PYR₁₁PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furan-PYR₁₄PF₆:

-   -   1) Furan-PYR₁₄Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Furan-PYR₁₄PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furoyl-PYR₁₁PF₆:

-   -   1) Furoyl-PYR₁₁Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Furoyl-PYR₁₁PF₆     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Benzenesulfonyl-PYR₁₁PF₆:

-   -   1) Benzenesulfonyl-PYR₁₁Cl in Step 1 is added to an equal weight         of acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Benzenesulfonyl-PYR₁₁PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of p-Toluenesulfonyl-PYR₁₁PF₆:

-   -   1) p-Toluenesulfonyl-PYR₁₁Cl in Step 1 is added to an equal         weight of acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form p-Toluenesulfonyl-PYR₁₁PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Benzyl-PIP_(IEE)PF₆:

-   -   1) Benzyl-PIP_(IEE)Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Benzyl-PIP_(IEE)PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furan-PIP₁₄PF₆:

-   -   1) Furan-PIP₁₄Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Furan-PIP₁₄PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furoyl-PIP₁₁PF₆:

-   -   1) Furoyl-PIP₁₁Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone     -   6) Recrystallized to form Furoyl-PIP 11PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Benzyl-TEA_(IEE)PF₆:

-   -   1) Benzyl-TEA_(IEE)Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Benzyl-TEA_(IEE)PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furan-TEA₁₄PF₆:

-   -   1) Furan-TEA₁₄Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Furan-TEA₁₄PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm

With reference to FIG. 6A/Table 6, the synthesis of Furoyl-TEA₁₁PF₆:

-   -   1) Furoyl-TEA₁₁Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone     -   6) Recrystallized to form Furoyl-TEA₁₁PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm

With reference to FIG. 6A/Table 6, the synthesis of Benzyl-MIM_(IEE)PF₆:

-   -   1) Benzyl-MIM_(IEE)Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 25° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Benzyl-MIM_(IEE)PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furan-MIM₁₄PF₆:

-   -   1) Furan-MIM₁₄Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 25° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Furan-MIM₁₄PF₆     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6A/Table 6, the synthesis of Furoyl-MIM₁₁PF₆:

-   -   1) Furoyl-MIM₁₁Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 25° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Furoyl-MIM₁₁PF₆     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-MPE₁₁PF₆:

-   -   1) Furoyl-MPE₁₁Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 45° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Furoyl-MPE₁₁PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-PYO₁₁PF₆.

-   -   1) Furoyl-PYO₁₁Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium hexafluorophosphate is added.     -   3) Stir at 45° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Furoyl-PYO₁₁PF₆.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-PYR₁₁BF₄:

-   -   1) Furoyl-PYR₁₁Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium tetrafluoroborate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Furoyl-PYR₁₁BF₄.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-PYR₁₁FSI.

-   -   1) Furoyl-PYR₁₁Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of lithiumbis(fluorosulfonyl)imide is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate lithium chloride LiCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Furoyl-PYR₁₁FSI.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-PYR₁₁TFSI.

-   -   1) Furoyl-PYR₁₁Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of lithium bis(trifluoromethane)sulfonamide         is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate lithium chloride LiCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Furoyl-PYR₁₁TFSI.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-PYR₁₁CF₃BF₃.

-   -   1) Furoyl-PYR₁₁Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of lithium trifluoromethyltrifluoroborate is         added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate lithium chloride LiCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Furoyl-PYR₁₁CF₃BF₃.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-PYR₁₁POF₂:

-   -   1) Furoyl-PYR₁₁Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of lithium difluorophosphate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate lithium chloride LiCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Furoyl-PYR₁₁POF₂.     -   7) The product is filtered, purified, and dried in a vacuum oven         at 60° C. until its water content is less than 20 ppm.

With reference to FIG. 6B/Table 6, the synthesis of Furoyl-PYR₁₁MeSO₄:

-   -   1) Furoyl-PYR₁₁Cl in Step 1 is added to an equal weight of         acetone.     -   2) Same mole number of potassium methyl sulfate is added.     -   3) Stir at 70° C. for 12 hours.     -   4) White precipitate potassium chloride KCl is filtered.     -   5) Remaining liquid is distilled under reduced pressure to         remove the acetone.     -   6) Recrystallized to form Furoyl-PYR₁₁MeSO₄:

The product is filtered, purified, and dried in a vacuum oven at 60° C. until its water content is less than 20 ppm

Embodiment 3

According to the maximum solubility, an ionic liquid with the two-core cationic chain or an ionic liquid with aromatic bonded to cation is added to a non-aqueous electrolyte. The amount of ionic liquid is about 10-15 wt. % of the electrolyte. Then, a linear sweep voltammetry (LSV) is conducted using the AutoLab 302N electrochemistry to obtain the maximum oxidation potential of the electrolyte.

Testing Conditions of LSV:

working electrode Pt, reference electrode Li, counter electrode Li, scan voltage range 0.5˜5.0 V, scan rate 0.03 V/s.

-   1. Traditional ionic liquid with aromatic heterocycle:     1-propyl-1-methylpyrrolidium hexafluorophosphate (PYR₁₃PF₆)     -   Electrolyte: 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+15 wt.         % PYR₁₃PF₆     -   With reference to FIGS. 7A and 7B, the LSV test shows that the         lithium deposition/dissolution reaction at low potential. A         corrosion current greater than 5×10⁻⁵ (Amp.) occurred at the         high potential of 4.742V in the first cycle. That is an         oxidation reaction, which means that the maximum oxidation         potential of the organic electrolyte with adding 15 wt. %         PYR₁₃PF₆ is 4.742 V. The potential window of that is about         0-4.742 V. There is no side reaction in this electrolyte within         this working voltage range. -   2. Two-core cationic chain ionic liquid: 1,5 bis(1-methylpyrrolidium     1-yl) pentane dihexafluorophosphate [DiPYR₁₅(PF₆)₂], 1,8     bis(1-methylpyrrolidium 1-yl) octane dihexafluorophosphate     [DiPYR₁₈(PF₆)₂]     -   Electrolyte:         -   (a) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+10 wt. %             DiPYR₁₅(PF₆)₂,         -   (b) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+10 wt. %             DiPYR₁₈(PF₆)₂         -   With reference to FIGS. 8A and 8B, the LSV test showed that             the lithium deposition/dissolution reaction also occurs at             low potential. The corrosion current greater than 5×10⁻⁵             (Amp.) occurred at the high potential of 4.922V in the first             cycle. This means that the maximum oxidation potential of             the organic electrolyte with 10 wt. % DiPYR₁₅(PF₆)₂ added is             4.922V. The potential window is about 0-4.922 V which             indicates that the addition of DiPYR₁₅(PF₆)₂ can increase             the maximum oxidation potential of the electrolyte, reduces             the dissociation reaction under the high working voltage,             and inhibits the growth of internal impedance in the             lithium-ion battery.         -   With reference to FIGS. 9A and 9B, the LSV test shows that             there was no corrosion current greater than 5×10⁻⁵ (Amp.) at             a high voltage of 5.02 V in the first cycle. This means that             the maximum oxidation potential of organic electrolyte with             adding 10 wt. % DiPYR₁₈(PF₆)₂ is greater than 5.0V. It             indicates that the addition of DiPYR₁₈(PF₆)₂ can increase             the maximum oxidation potential of the electrolyte with the             ability of withstanding high voltage being better than that             of the addition of DiPYR₁₅(PF₆)₂. -   4. Replacing the alkyl chain Y with other functional groups,     replacing the cation X₁ and X₂ with other heterocyclic aromatic or     amine, or replacing the anion Z₁ and Z₂. Taking the following ionic     liquids with two-core cationic chain as examples: bis     [2-(1-methylpyrrolidinium 1-yl) ethyl] ether dihexafluorophosphate     [DiPYR_(IEE)(PF₆)₂], 1,5-(1-methylpyrrolidium     1-yl)(1-methylpiperidinium) 1-yl) pentane dihexafluorophosphate     [PYRPIP₁₅(PF₆)_(2], 1,5)-bis (1-methylpiperidinium 1-yl) pentane     dihexafluorophosphate [DiPIP₁₅(PF₆)_(2], 1,5)-bis     (1-methylpyrrolidium 1-yl) pentane (hexafluorophosphate)     (tetrafluoroborate) [DiPYR₁₅(PF₆)(BF₄)], 1,5-(1-methylpyrrolidium     1-yl) (1-methyl-imidazolium-3-yl) pentane dihexafluorophosphate     [PYRMIM₁₅(PF₆)₂].     -   Electrolyte:         -   (a) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+15 wt. %             DiPYR_(IEE)(PF₆)₂,         -   (b) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+10 wt. %             PYRPIP₁₅(PF₆)₂,         -   (c) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+10 wt. %             DiPIP₁₅(PF₆)₂,         -   (d) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+15 wt. %             DiPYR₁₅(PF₆)(BF₄),         -   (e) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+10 wt. %             PYRMIM₁₅(PF₆)₂.         -   With reference to FIGS. 11A to 14B, the LSV test shows that             the maximum oxidation potentials of the above four ionic             liquids in the initial cycle are 4.774V, 4.929V, 4.895V and             greater than 5.0V, respectively which indicates that the             alkyl functional group Y, heterocyclic aromatic cation X₁             and X₂, and anion Z₁ and Z₂ can change the maximum oxidation             potential of the electrolyte. Among them, the electrolyte             with DiPYR₁₅(PF₆)(BF₄) added has the best ability of             withstanding high voltage. In addition, by replacing the             cations X₁ and X₂ with methylimidazole (MIM) and morpholine             (MPE) cations with result in extremely unstable             electrolytes, and the highest oxidation potential of that             cannot be determined. For the other types of ionic liquids             with two-core cationic chain and the aromatic bonded to             cation, the maximum oxidation potential of their             electrolytes at the LSV test are shown in FIG. 15 /Table 7             and FIG. 16 /Table 8.         -   With reference to FIGS. 15A, 15B and 15C, the maximum             oxidation potential must be greater than 4.7V to be             considered to present an improvement. Any added amount of             ionic liquid (as detailed below) would be of an amount of             10-15 wt. % in the organic electrolyte:         -   The maximum oxidation potential (V) of an organic             electrolyte, 1M LiPF6+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC, as             a control sample is 4.652V.         -   The maximum oxidation potential (V) of DiPYR₁₄(PF₆)₂, X₁ is             NMPD, X₂ is NMPD, Y is Butane, C4, Z₁ is PF₆, Z₂ is PF₆ is             4.906V.         -   The maximum oxidation potential (V) of DiPYR₁₅(PF₆)₂, X₁ is             NMPD, X₂ is NMPD, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             4.922V.         -   The maximum oxidation potential (V) of DiPYR₁₆(PF₆)₂, X₁ is             NMPD, X₂ is NMPD, Y is Hexane, C6, Z₁ is PF₆, Z₂ is PF₆ is             4.872V.         -   The maximum oxidation potential (V) of DiPYR₁₈(PF₆)₂, X₁ is             NMPD, X₂ is NMPD, Y is Octane, C8, Z₁ is PF₆, Z₂ is PF₆ is             >5.0V.         -   The maximum oxidation potential (V) of DiPIP₁₅(PF₆)₂, X₁ is             MPIP, X₂ is MPIP, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             4.895V.         -   The maximum oxidation potential (V) of DiPIP₁₈(PF₆)₂, X₁ is             MPIP, X₂ is MPIP, Y is Octane, C8, Z₁ is PF₆, Z₂ is PF₆ is             4.963V.         -   The maximum oxidation potential (V) of DiPYR₁₅(PF₆)(BF₄), X₁             is NMPD, X₂ is NMPD, Y is Pentane, C5, Z₁ is PF₆, Z₂ is BF₄             is >5.0V.         -   The maximum oxidation potential (V) of DiPYR₁₅(PF₆)(BF₄), X₁             is NMPD, X₂ is NMPD, Y is Octane, C8, Z₁ is PF₆, Z₂ is BF₄             is >5.0V.         -   The maximum oxidation potential (V) of DiPIP₁₅(PF₆)(BF₄), X₁             is MPIP, X₂ is MPIP, Y is Pentane, C5, Z₁ is PF₆, Z₂ is BF₄             is 4.955V.         -   The maximum oxidation potential (V) of DiPIP₁₈(PF₆)(BF₄), X₁             is MPIP, X₂ is MPIP, Y is Octane, C8, Z₁ is PF₆, Z₂ is BF₄             is >5.0V.         -   The maximum oxidation potential (V) of PYRPIP₁₅(PF₆)₂, X₁ is             NMPD, X₂ is MPIP, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             4.929V.         -   The maximum oxidation potential (V) of PYRTEA₁₅(PF₆)₂, X₁ is             NMPD, X₂ is TEA, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             >5.0V.         -   The maximum oxidation potential (V) of PYRMPE₁₅(PF₆)₂, X₁ is             NMPD, X₂ is MPE, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             4.653V.         -   The maximum oxidation potential (V) of PYRMIM₁₅(PF₆)₂, X₁ is             NMPD, X₂ is MIM, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             unavailable.         -   The maximum oxidation potential (V) of PYRPYO₁₅(PF₆)₂, X₁ is             NMPD, X₂ is PYO, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             4.782V.         -   The maximum oxidation potential (V) of PIPTEA₁₅(PF₆)₂, X₁ is             MPIP, X₂ is TEA, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             4.968V.         -   The maximum oxidation potential (V) of PIPMPE₁₅(PF₆)₂, X₁ is             MPIP, X₂ is MPE, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             4.372V.         -   The maximum oxidation potential (V) of PIPMIM₁₅(PF₆)₂, X₁ is             MPIP, X₂ is MIM, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             unavailable.         -   The maximum oxidation potential (V) of PIPPYO₁₅(PF₆)₂, X₁ is             MPIP, X₂ is PYO, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             4.739V.         -   The maximum oxidation potential (V) of TEAMPE₁₅(PF₆)₂, X₁ is             TEA, X₂ is MPE, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             4.562V.         -   The maximum oxidation potential (V) of TEAMIM₁₅(PF₆)₂ X₁ is             TEA, X₂ is MIM, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             unavailable.         -   The maximum oxidation potential (V) of TEAPYO₁₅(PF₆)₂, X₁ is             TEA, X₂ is PYO, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             4.809V.         -   The maximum oxidation potential (V) of MIMMPE₁₅(PF₆)₂, X₁ is             MIM, X₂ is MPE, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             unavailable.         -   The maximum oxidation potential (V) of MIMPYO₁₅(PF₆)₂, X₁ is             MIM, X₂ is PYO, Y is Pentane, C5, Z₁ is PF₆, Z₂ is PF₆ is             unavailable.         -   The maximum oxidation potential (V) of PYRPIP₁₅(PF₆)(PF₄),             X₁ is NMPD, X₂ is MPIP, Y is Pentane, C5, Z₁ is PF₆, Z₂ is             BF₄ is >5.0V.         -   The maximum oxidation potential (V) of PYRTEA₁₅(PF₆)(PF₄),             X₁ is NMPD, X₂ is TEA, Y is Pentane, C5, Z₁ is PF₆, Z₂ is             BF₄ is >5.0V.         -   The maximum oxidation potential (V) of PYRPYO₁₅(PF₆)(PF₄),             X₁ is NMPD, X₂ is PYO, Y is Pentane, C5, Z₁ is PF₆, Z₂ is             BF₄ is 4.833V.         -   The maximum oxidation potential (V) of PIPTEA₁₅(PF₆)(PF₄),             X₁ is MPIP, X₂ is TEA, Y is Pentane, C5, Z₁ is PF₆, Z₂ is             BF₄ is 4.928V.         -   The maximum oxidation potential (V) of PIPPYO₁₅(PF₆)(PF₄),             X₁ is MPIP, X₂ is PYO, Y is Pentane, C5, Z₁ is PF₆, Z₂ is             BF₄ is 4.760V.         -   The maximum oxidation potential (V) of TEAPYO₁₅(PF₆)(PF₄),             X₁ is TEA, X₂ is PYO, Y is Pentane, C5, Z₁ is PF₆, Z₂ is BF₄             is 4.858V.         -   The maximum oxidation potential (V) of DiPYR₁₅(TFSI)(FSI),             X₁ is NMPD, X₂ is NMPD, Y is Pentane, C5, Z₁ is TFSI, Z₂ is             FSI is 4.937V.         -   The maximum oxidation potential (V) of DiPIP₁₅(TFSI)(FSI),             X₁ is MPIP, X₂ is MPIP, Y is Pentane, C5, Z₁ is TFSI, Z₂ is             FSI is 4.912V.         -   The maximum oxidation potential (V) of PYRPIP₁₅(TFSI)(FSI),             X₁ is NMPD, X₂ is MPIP, Y is Pentane, C5, Z₁ is TFSI, Z₂ is             FSI is 4.938V.         -   The maximum oxidation potential (V) of PYRTEA₁₅(TFSI)(FSI),             X₁ is NMPD, X₂ is TEA, Y is Pentane, C5, Z₁ is TFSI, Z₂ is             FSI is >5.0V.         -   The maximum oxidation potential (V) of PIPTEA₁₅(TFSI)(FSI),             X₁ is MPIP, X₂ is TEA, Y is Pentane, C5, Z₁ is TFSI, Z₂ is             FSI is 4.953V.         -   The maximum oxidation potential (V) of             DiPYR₁₅(CF₃BF₃)(POF₂), X₁ is NMPD, X₂ is NMPD, Y is Pentane,             C5, Z₁ is CF₃BF₃, Z₂ is POF₂ is >5.0V.         -   The maximum oxidation potential (V) of             DiPIP₁₅(CF₃BF₃)(POF₂), X₁ is MPIP, X₂ is MPIP, Y is Pentane,             C5, Z₁ is CF₃BF₃, Z₂ is POF₂ is 4.935V.         -   The maximum oxidation potential (V) of             PYRPIP₁₅(CF₃BF₃)(POF₂), X₁ is NMPD, X₂ is MPIP, Y is             Pentane, C5, Z₁ is CF₃BF₃, Z₂ is POF₂ is >5.0V.         -   The maximum oxidation potential (V) of             PYRTEA₁₅(CF₃BF₃)(POF₂), X₁ is NMPD, X₂ is TEA, Y is Pentane,             C5, Z₁ is CF₃BF₃, Z₂ is POF₂ is >5.0V.         -   The maximum oxidation potential (V) of             PIPTEA₁₅(CF₃BF₃)(POF₂), X₁ is MPIP, X₂ is TEA, Y is Pentane,             C5, Z₁ is CF₃BF₃, Z₂ is POF₂ is 4.976V.         -   The maximum oxidation potential (V) of DiPYR₁₄(BF₄)(FSI), X₁             is NMPD, X₂ is NMPD, Y is Pentane, C5, Z₁ is BF₄, Z₂ is FSI             is 4.962V.         -   The maximum oxidation potential (V) of DiPIP₁₅(BF₄)(FSI), X₁             is MPIP, X₂ is MPIP, Y is Pentane, C5, Z₁ is BF₄, Z₂ is FSI             is 4.907V.         -   The maximum oxidation potential (V) of PYRPIP₁₅(BF₄)(FSI),             X₁ is NMPD, X₂ is MPIP, Y is Pentane, C5, Z₁ is BF₄, Z₂ is             FSI is >5.0V.         -   The maximum oxidation potential (V) of PYRTEA₁₅(BF₄)(FSI),             X₁ is NMPD, X₂ is TEA, Y is Pentane, C5, Z₁ is BF₄, Z₂ is             FSI is >5.0V.         -   The maximum oxidation potential (V) of PIPTEA₁₅(BF₄)(FSI),             X₁ is MPIP, X₂ is TEA, Y is Pentane, C5, Z₁ is BF₄, Z₂ is             FSI is 4.974V.         -   The maximum oxidation potential (V) of DiPYR_(IEE)(PF₆)₂, X₁             is NMPD, X₂ is NMPD, Y is iethyl ether, Z₁ is PF₆, Z₂ is PF₆             is 4.774V.         -   The maximum oxidation potential (V) of DiPYR_(IEC)(PF₆)₂, X₁             is NMPD, X₂ is NMPD, Y is Diethyl carbonate, C4, Z₁ is PF₆,             Z₂ is PF₆ is 4.825V.         -   The maximum oxidation potential (V) of DiPYR_(IPO)(PF₆)₂, X₁             is NMPD, X₂ is NMPD, Y is Pentan-3-one, Z₁ is PF₆, Z₂ is PF₆             is 4.833V.         -   The maximum oxidation potential (V) of DiPYR_(IEB)(PF₆)₂, X₁             is NMPD, X₂ is NMPD, Y is Diethyl butanedioate, Z₁ is PF₆,             Z₂ is PF₆ is 4.706V.         -   With reference to FIGS. 16A and 16B, again, the maximum             oxidation potential must be greater than 4.7V to be             considered to present an improvement. Any added amount of             ionic liquid (as detailed below) would be of an amount of             1-10 wt. % in the organic electrolyte:         -   The maximum oxidation potential (V) of an organic             electrolyte, 1M LiPF6+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC, as             a control sample is 4.652V.         -   The maximum oxidation potential (V) of PYR_(1BEE)PF₆ with X₁             is NMPD, Y & W are Benzyl ethyl ether, Z₁ is PF₆, is 4.739V.         -   The maximum oxidation potential (V) of PYR_(1BBE)PF₆ with X₁             is NMPD, Y & W are Benzyl butyl ether, Z₁ is PF₆, is 4.757V.         -   The maximum oxidation potential (V) of PYR_(1BZO)PF₆ with X₁             is NMPD, Y & W are Benzoyl, Z₁ is PF₆, is 4.746V.         -   The maximum oxidation potential (V) of PYR_(1PHC)PF₆ with X₁             is NMPD, Y & W are Phenacyl, Z₁ is PF₆, is 4.773V.         -   The maximum oxidation potential (V) of PYR_(1FRA)PF₆ with X₁             is NMPD, Y & W are 2-Furan, Z₁ is PF₆, is 4.722V.         -   The maximum oxidation potential (V) of PYR_(14FRA)PF₆ with             X₁ is NMPD, Y & W are 2-ButylFuran, Z₁ is PF₆, is 4.736V.         -   The maximum oxidation potential (V) of PYR_(1FRO)PF₆ with X₁             is NMPD, Y & W are 2-Furoyl, Z₁ is PF₆, is 4.829V.         -   The maximum oxidation potential (V) of PYR_(1BSF)PF₆ with X₁             is NMPD, Y & W are Benzenesulfonyl, Z₁ is PF₆, is 4.817V.         -   The maximum oxidation potential (V) of PYR_(1TSF)PF₆ with X₁             is NMPD, Y & W are p-Toluenesulfonyl, Z₁ is PF₆, is 4.801V.         -   The maximum oxidation potential (V) of PIP_(1BEE)PF₆ with X₁             is MPIP, Y & W are Benzyl ethyl ether, Z₁ is PF₆, is 4.536V.         -   The maximum oxidation potential (V) of PIP_(14FRA)PF₆ with             X₁ is MPIP, Y & W are 2-ButylFuran, Z₁ is PF₆, is 4.622V.         -   The maximum oxidation potential (V) of PIP_(1FRO)PF₆ with X₁             is MPIP, Y & W are 2-Furoyl, Z₁ is PF₆, is 4.729V.         -   The maximum oxidation potential (V) of TEA_(1BEE)PF₆ with X₁             is TEA, Y & W are Benzyl ethyl ether, Z₁ is PF₆, is 4.389V.         -   The maximum oxidation potential (V) of TEA_(14FRA)PF₆ with             X₁ is TEA, Y & W are 2-ButylFuran, Z₁ is PF₆, is 4.443V.         -   The maximum oxidation potential (V) of TEA_(1FRO)PF₆ with X₁             is TEA, Y & W are 2-Furoyl, Z₁ is PF₆, is 4.738V.         -   The maximum oxidation potential (V) of MIM_(1BEE)PF₆ with X₁             is MIM, Y & W are Benzyl ethyl ether, Z₁ is PF₆, is             unavailable.         -   The maximum oxidation potential (V) of MIM_(14FRA)PF₆ with             X₁ is MIM, Y & W are 2-ButylFuran, Z₁ is PF₆, is             unavailable.         -   The maximum oxidation potential (V) of MIM_(14FRO)PF₆ with             X₁ is MIM, Y & W are 2-Furoyl, Z₁ is PF₆, is unavailable.         -   The maximum oxidation potential (V) of MPE_(1FRO)PF₆ with X₁             is MPE, Y & W are 2-Furoyl, Z₁ is PF₆, is unavailable.         -   The maximum oxidation potential (V) of PYO_(1FRO)PF₆ with X₁             is PYO, Y & W are 2-Furoyl, Z₁ is PF₆, is unavailable.         -   The maximum oxidation potential (V) of PYO_(1FRO)BF₄ with X₁             is NMPD, Y & W are 2-Furoyl, Z₁ is BF₄, is 4.926V.         -   The maximum oxidation potential (V) of PYR_(1FRO)FSI with X₁             is NMPD, Y & W are 2-Furoyl, Z₁ is FSI, is 4.877V.         -   The maximum oxidation potential (V) of PYR_(1FRO)TFSI with             X₁ is NMPD, Y & W are 2-Furoyl, Z₁ is TFSI, is 4.917V.         -   The maximum oxidation potential (V) of PYR_(1FRO)CF₃BF₃ with             X₁ is NMPD, Y & W are 2-Furoyl, Z₁ is CF₃BF₃, is 4.958V.         -   The maximum oxidation potential (V) of PYR_(1FRO)POF₂ with             X₁ is NMPD, Y & W are 2-Furoyl, Z₁ is POF₂, is 4.923V.         -   The maximum oxidation potential (V) of PYR_(1FRO)MeSO₄ with             X₁ is NMPD, Y & W are 2-Furoyl, Z₁ is MeSO₄, is 4.607V.

With reference to Tables 7 and 8, the LSV test shows that the highest oxidation potential of the related electrolyte cannot be determined, when the cation X₁ and X₂ of two-core cationic chain ionic liquid are methylimidazole (MIM) and morpholine (MPE) cations. There is no obvious improvement on the ability of withstanding high voltage. In addition, while the cation X₁ of ionic liquid with aromatic bonded to cation is the N-methyl pyrrolidine (NMPD), the maximum oxidation potential of related electrolyte is higher than 4.7 V, which shows an enhancement on the withstanding high voltage of electrolyte.

Embodiment 4

According to the maximum solubility, an ionic liquid with the two-core cationic chain or an ionic liquid with aromatic bonded to cation is added to a non-aqueous electrolyte. The amount of ionic liquid is about 10-15 wt. % of the electrolyte. Then, a cyclic voltammetry (CV) is conducted using the AutoLab 302N electrochemistry instrument to understand the oxidation-reduction reaction between the electrolyte and the graphite anode under different voltages.

CV Test Conditions:

Working electrode: (Anode material) meso carbon micro bead

-   -   MCMB:SuperP:CMC:SBR=95.5:1.0:1.5:2.0

Reference electrode Li, counter electrode Li, scan voltage range 0˜2.5V, scan rate 1 mV/s.

-   1. Traditional cationic ionic liquid with aromatic heterocycle:     1-propyl-1-methylpyrrolidium hexafluorophosphate (PYR₁₃PF₆)     -   Electrolyte: 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+15 wt.         % PYR₁₃PF₆         -   With reference to FIG. 17 , the CV test shows that a             reduction peak appeared at 0.7-1.0 V when 15 wt. % PYR₁₃PF₆             ionic liquid was added to the electrolyte. The reason being             that the PYR₁₃ ⁺ cations are intercalated into the layered             structure on the surface of MCMB, preventing lithium ions             from migrating into the layered structure. This leads to the             generation of lithium precipitation on the surface of anode,             thereby increasing the interface impedance, and causing a             decline in the cycle stability of battery. -   2. Two-core cationic chain ionic liquid: 1,5 Bis(1-methylpyrrolidium     1-yl) pentane dihexafluorophosphate [DiPYR₁₅(PF₆)₂], 1,8     Bis(1-methylpyrrolidium 1-yl) octane dihexafluorophosphate     [DiPYR₁₈(PF₆)₂]     -   Electrolyte: (a) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+10         wt. % DiPYR₁₅(PF₆)₂, (b) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt.         % VC+10 wt. % DiPYR₁₈(PF₆)₂         -   With reference to FIGS. 18A and 18B, there was no reduction             peak at 0.7-1.0 V when 10 wt. % of DiPYR₁₅(PF₆)₂ or 10 wt. %             of DiPYR₁₈(PF₆)₂ ionic liquid is added to the electrolyte.             This indicates that when the molecular weight and functional             group of the cation is sufficiently large, the ionic liquid             would not be able to intercalate into the MCMB layered             structure. The ionic liquids with two-core cationic chain or             the cation ionic liquid with aromatic bonded to the cation             according to the invention, in which the two cations are             linked together, their molecular weight is increased             sufficiently so as to result in poor intercalation into the             anode material. -   3. Replacement of the alkyl chain Y with other functional groups,     and replacement of the cation X₁ and X₂ with other heterocyclic     aromatic or amine, and replacement of other anionic groups Z₁ and     Z₂: Taking the following two ionic liquids with dual core cationic     chain as examples: bis[2-(1-methylpyrrolidinium 1-yl) ethyl] ether     dihexafluorophosphate [DiPYR_(IEE)(PF₆)₂], 1,5-(1-methylpyrrolidium     1-yl)(1-methylpiperidinium 1-yl) pentane dihexafluorophosphate     [PYRPIP₁₅ (PF₆)_(2], 1,5)-bis(1-methylpiperidinium 1-yl) pentane     dihexafluorophosphate [DiPIP₁₅(PF₆)₂], 1,5-bis(1-methylpyrrolidium     1-yl) pentane (hexafluorophosphate) (tetrafluoroborate)     [DiPYR₁₅(PF₆)(BF₄)]     -   Electrolyte: (a) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+15         wt. % DiPYR_(IEE)(PF₆)₂, (b) 1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1         wt. % VC+10 wt. % PYRPIP₁₅(PF₆)₂, (c) 1M LiPF₆+EC:DMC:EMC=1:1:1         (vol.)+1 wt. % VC+10 wt. % DiPIP₁₅(PF₆)₂, (d) 1M         LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+15 wt. %         DiPYR_(is)(PF₆)(BF₄)     -   With reference to FIGS. 19A to 19D, there is no reduction peak         at 0.7-1.0 V when DiPYR_(IEE)(PF₆)₂, DiPIPPYR₁₅(PF₆)₂,         DiPIP₁₅(PF₆)₂ or DiPYR₁₅(PF₆)(BF₄) ionic liquid is added to the         electrolyte. It indicates that the molecular weight of the         two-core structure and its functional group is sufficiently         large to minimize intercalation into the MCMB layered structure,         yet does not hinder the intercalation and exfoliation of lithium         ions. The interface impedance on the surface of the anode is         reduced.

Embodiment 5

A pouch cell battery with a capacity of 40 Ah with the ionic liquid added to the organic electrolyte is used to verify or authenticate the composition and structure of a solid electrolyte interface film (SEI) on the surface of the anode during the charging and discharging processes of the lithium ion battery with the two-core structure ionic liquid according to the invention developed in this patent. In the test, the battery undergo splint formation to charge to 3.5 V, and then discharge with a small current to 2.0 V. The battery is disassembled in an inert atmosphere glove box with the anode being removed. The removed anode is soaked in the dimethyl carbonate (DMC) for about 15 minutes, followed by shaking the anode to remove any remaining lithium salt. The anode is then left to dry in the shade.

The National Synchrotron Radiation Research Center (NSRRC) Beamline at the 20A1 station is used to perform Soft X-ray Absorption Spectroscopy (sXAS) to verify the composition and structure of the SEI film on the surface of anode. The oxygen K-edge absorption spectrum includes total electron yield (TEY) and total fluorescence yield (TFY). In TEY, due to the restraint of the coulomb force between electrons, it would not be easy for the electrons deep inside the electrode to reach the electrode surface and be received. Only the electrons close to the surface are attracted by the applied bias and are received by the receiver. As such, the structure of the material in the range of 10 nm on a surface can be analyzed. As for the TFY, fluorescence is composed of photons, it will not be restricted by the coulomb force. It is useful in detecting/analyzing electronic structure deeper within the electrode, i.e. in the range of 200 nm on a surface.

Synchrotron sXAS Experiment Conditions:

-   1. A pouch cell of lithium iron phosphate (LFP) battery with the     capacity of 40 Ah. -   2. Splint formation: charge at the 0.01 C for 3 hours, charge at the     0.1 C to 3.6 V, and then discharge at the 0.1 C to 2.0 V; -   3. The anode material is meso carbon micro bead     MCMB:SuperP:CMC:SBR=95.5:1.0:1.5:2.0; -   4. Electrolyte: (a) Organic electrolyte (OE): 1M     LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC, (b) 1M     LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+6 wt. % PYRTEA₁₅(PF₆)₂, (c)     1M LiPF₆+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+6 wt. %     DiPYR₁₅(PF₆)₂, (d) 1M LiPF6+EC:DMC:EMC=1:1:1 (vol.)+1 wt. % VC+6 wt.     % DiPYR_(IEE)(PF₆)₂; -   5. Oxygen K-edge total electron yield (TEY), Energy range: 525˜555     eV.

With reference to FIG. 20 , the standard Li₂CO₃ product is tested by X-ray absorption spectrum O K-edge TEY. The characteristic peak positions of C═O (π*bond) and C—O (α*bond) of CO₃ ²⁻ are at 533.5 eV, 538.7 eV and 542 eV, respectively. A pouch cell of LFP battery with the capacity of 40 Ah with organic electrolyte (OE) without adding any ionic liquid of the invention is charged at the 0.01 C for 3 hours, charge at the 0.1 C to 3.6 V, and then discharged at the 0.1 C to 2.0 V, the SEI film produced by the reaction of interface between the electrolyte and anode is detected. The TEY test result shows that the characteristic curve is similar to that of the standard Li₂CO₃, and an obvious characteristic peak appears at 533.5 eV, indicating that the structure of SEI film produced by the OE electrolyte is mainly Li₂CO₃.

Again with reference to FIG. 20 , the ionic liquid with dual core structure, including PYRTEA₁₅(PF₆)₂, DiPYR₁₅(PF₆)₂ and DiPYR_(IEE)(PF₆)₂ are added at 6 wt. % to the OE electrolyte respectively. Three samples of pouch cell LFP battery, capacity of 40 Ah is used, with OE+PYRTEA₁₅(PF₆)₂, organic electrolyte (OE)+DiPYR₁₅(PF₆)₂ and OE+DiPYR_(IEE)(PF₆)₂ respectively. The surface of the anodes is tested by the sXAS absorption spectrum O K-edge TEY. Each of them shows an obvious Li₂CO₃ characteristic peak at 533.5 eV, but the other peaks also appear at the position of 532˜533 eV. The main components includes the characteristic peaks of COH at 531.7 eV and the O—O of organic lithium salt ROCO₂Li at 532.5 eV, which means in each of the three samples, a thin layer of organic film is formed in the range of ˜5 nm on the surface of anode. The amount of organic film formed in the three samples are of the order of OE+DiPYR_(IEE)(PF₆)₂>OE+DiPYR₁₅(PF₆)₂>OE+PYRTEA₁₅(PF₆)₂. It is concluded that the addition of the ionic liquids according to the invention not only inhibits the intercalation at the anode, but also result in the formation of a thin layer of organic film on the anode surface. By adding an appropriate amount of the ionic liquid to the electrolyte, the interface resistance will be reduced and the thermal stability of the overall lithium-ion battery will be improved as the ionic liquid has high melting point and is an effective flame retardant.

Embodiment 6

The performance of LFP batteries with the pouch cell of 40 Ah and 60 Ah with different electrolyte formulations.

Preparation of Cathode Sheet

Cathode active material: LFP, binder: polyvinylidene fluoride (PVDF), conductive agent: carbon black (Super P®) are mixed according to the weight ratio of LFP:Super P:PVDF=96:2:2, followed by adding the solvent: N-methyl pyrrolidone. It is then stirred and dispersed uniformly in a vacuum stirring machine to obtain the cathode slurry. The cathode slurry is uniformly coated on an aluminum foil by a coating machine, and the solvent is removed by the drying in hot air. The cathode sheet is obtained by cold pressing and slitting.

Preparation of Anode Sheet

Anode active material: meso carbon micro bead (MCMB), conductive agent: carbon black (Super P), thickener: sodium carboxymethyl cellulose (CMC), binder: styrene butadiene rubber (SBR) emulsion are mixed in a ratio of MCMB:Super P:CMC:SBR=95.5:1.0:1.5:2.0 with deionized water as solvent. It is stirred and dispersed uniformly in a vacuum stirring machine to obtain the anode slurry. The anode slurry is uniformly coated on the copper foil by a coating machine, and the solvent is removed by the drying in hot air. Anode sheet is obtained by cold pressing and slitting.

Preparation of Electrolyte

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 mole/L (M) of LiPF₆ in the specified sequence. The electrolyte is formed after mixing. Electrolyte with different film-forming agent (A), stabilizer (B), ionic liquid (C) are shown in FIG. 21A, FIG. 21B and Table 9.

With Reference to FIG. 21A, Electrolyte Formula 1:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A): VC: Vinylene carbonate at 1 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 2:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 3:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt. %, the stabilizer (B) is EPFCP: Ethoxy(pentafluoro)cyclotriphosphazene at 3 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 4:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt. %, the ionic liquid (C) is PYR₁₃PF₆ at 5 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 5:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt. %, the stabilizer (B) is HFCP: Hexafluoro cyclotriphosphazene at 2.9 wt. %, the ionic liquid (C) is PYR₁₃PF₆ at 5 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 6:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt. %, the stabilizer (B) is EPFCP: Ethoxy(pentafluoro)cyclotriphosphazene at 2.9 wt. %, the ionic liquid (C) is PYR₁₃PF₆ at 5 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 7:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt. %, the stabilizer (B) is EPFCP: Ethoxy(pentafluoro)cyclotriphosphazene at 2.9 wt. %, the ionic liquid (C) is PYR₁₃PF₆ at 10 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 8:

LFP Batteries with the Pouch Cell of 40 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt. %, the stabilizer (B) is EPFCP: Ethoxy(pentafluoro)cyclotriphosphazene at 2.9 wt. %, the ionic liquid (C) is PYR₁₃PF₆ at 15 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 9:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), ionic liquid (C) and 1 M of LiPF6 in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt. %, the stabilizer, the ionic liquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 10:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt. %, the stabilizer (B) is HFCP at 2 wt. %, the ionic liquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 11:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt. %, the stabilizer (B) is EPFCP at 2 wt. %, the ionic liquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 12:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt. %, the stabilizer (B) is EPFCP at 2 wt. %, the ionic liquid (C) is DiPYR₁₅(PF₆)₂ at 8 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 13:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 1 wt. %, the stabilizer (B) is EPFCP at 2 wt. %, the ionic liquid (C) is DiPYR₁₅(PF₆)₂ at 10 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 14:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 2 wt. % and FEC: Fluoroethylene carbonate at 1 wt. %, the stabilizer (B) is EPFCP at 2 wt. %, the ionic liquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21A, Electrolyte Formula 15:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 3 wt. % and FEC: Fluoroethylene carbonate at 1 wt. %, the stabilizer (B) is EPFCP at 2 wt. %, the ionic liquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21B, Electrolyte Formula 16:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 2 wt. %, the stabilizer (B) is EPFCP at 2 wt. %, the ionic liquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21B, Electrolyte Formula 17:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF6 in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 3 wt. %, the stabilizer (B) is EPFCP at 2 wt. %, the ionic liquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21B, Electrolyte Formula 18:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 2 wt. %, the stabilizer (B) is EPFCP at 2.8 wt. %, the ionic liquid (C) is Furoyl-PYR₁₁(PF₆)₂ at 6 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21B, Electrolyte Formula 19:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 2 wt. %, the stabilizer (B) is EPFCP at 2.8 wt. %, the ionic liquid (C) is DiPYR₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21B, Electrolyte Formula 20:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 2 wt. %, the stabilizer (B) is EPFCP at 2.8 wt. %, the ionic liquid (C) is DiPYR_(IEE)(PF₆)₂ at 6 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21B, Electrolyte Formula 21:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 2 wt. %, the stabilizer (B) is EPFCP at 2.5 wt. %, the ionic liquid (C) is PYRPIP_(IEE)(PF₆)₂ at 6 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21B, Electrolyte Formula 22:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 2 wt. %, the stabilizer (B) is EPFCP at 2.5 wt. %, the ionic liquid (C) is DiPIP₁₅(PF₆)₂ at 6 wt. %. The electrolyte is formed after mixing.

With Reference to FIG. 21B, Electrolyte Formula 23:

LFP Batteries with the Pouch Cell of 60 Ah

Organic solvent (OE): Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed according to the weight ratio of EC:DMC:EMC=1:1:1. The lithium salt LiPF₆ is dissolved in the organic solvent followed by adding film-forming agent (A), stabilizer (B), ionic liquid (C) and 1 M of LiPF₆ in the specified sequence. Film-forming agent (A) is VC: Vinylene carbonate at 1 wt. % and FEC: Fluoroethylene carbonate at 2 wt. %, the stabilizer (B) is EPFCP at 2.5 wt. %, the ionic liquid (C) is DiPYR₁₅(PF₆)(BF₄) at 6 wt. %. The electrolyte is formed after mixing.

Formation of LFP Battery

With reference to FIGS. 22A and 22B, cathode sheet, anode sheet, and separator are laminated. Ultrasonic welding is used to attach the conductive lugs to obtain a bare battery cell. The bare battery cell is inserted into the aluminum-plastic film pit. After encapsulation, any one of the electrolytes 1 to 23 as detailed in FIG. 21 /Table 9 is injected. The pouch is sealed. The pouch battery is allowed to stand, undergo cold pressing, formation, exhausting, capacity testing, aging and other processes, the pouch cell of LFP battery with the capacity of 40˜60 Ah is obtained. The specification of battery is shown in the figure below.

Self-extinguishing time SET of electrolyte for battery prepared according to FIG. 21 /Table 9

1.2 g of each electrolyte as detailed in FIG. 21 /Table 9 is placed onto a glass fiber filter with a diameter of 47 mm and a thickness of 0.5 mm. The electrolyte is ignited and burnt. The time from ignition to extinguishment per gram of electrolyte in each of the batteries in FIG. 21 /Table 9 is recorded, the unit is sec/g, referred to as the self-extinguishing time (Self-extinguish time, SET). Each of Electrolyte formula 1 to 23 are tested respectively. The results are produced in FIG. 10 .

Performance Test of Lithium-Ion Battery Prepared According to FIG. 21 /Table 9

At 25° C., each LFP battery with any one of electrolyte 1 to 23 is charged to 3.6 V at a constant current of 0.5 C followed by charging the battery at a constant voltage of 3.6 V until the current drops to 0.05 C, and then discharged to 2.5 V at a constant current of 0.5 C. This is one charge-discharge cycle and this is the first discharge capacity of lithium-ion battery. Under the aforementioned charge and discharge conditions, the lithium-ion battery is subjected to multiple cycles of testing until the discharge capacity reaches 80% of the first discharge capacity (The capacity retention (C.R.) being 80%). The number of charge and discharge cycles until C.R.=80% of respective batteries is recorded. The results are produced in FIG. 10 . The lithium ion battery with different electrolyte formula (1 to 23) are tested respectively.

Internal Impedance Test

The internal impedance AC IR value of the lithium ion battery with any one of electrolyte formula 1 to 23 as detailed in Table 9 is detected by HIOKI BT3561 battery internal resistance meter and the results are recorded in FIG. 10 .

Referring to FIGS. 23A and 23B, it shows the performance of LFP battery in the form of pouch cell 40 Ah (No. 1 to 8) and the performance of LFP battery in the form of pouch cell 60 Ah (No. 9 to 23).

The self-extinguishing time, internal impedance and performance of each battery with any one of the electrolyte formulae listed in FIG. 23 are recorded in FIG. 10 . The batteries are given the same number (No.) as the number of assigned to each electrolyte formulae as detailed in FIG. 23 .

With reference to FIG. 23A, No. 1, the LFP battery 40 Ah with electrolyte formula 1 has a self-extinguishing time of 63 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 3.27 mΩ and the charge/discharge cycle number under 25 degree C. is 1359.

In No. 2, the LFP battery 40 Ah with electrolyte formula 2 has a self-extinguishing time of 58 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 3.05 mΩ and the charge/discharge cycle number under 25 degree C. is 1492.

In No. 3, the LFP battery 40 Ah with electrolyte formula 3 has a self-extinguishing time of 45 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 2.92 mΩ and the charge/discharge cycle number under 25 degree C. is 1553.

In No. 4, the LFP battery 40 Ah with electrolyte formula 4 has a self-extinguishing time of 36 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 3.48 mΩ and the charge/discharge cycle number under 25 degree C. is 1265.

In No. 5, the LFP battery 40 Ah with electrolyte formula 5 has a self-extinguishing time of 22 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 3.12 mΩ and the charge/discharge cycle number under 25 degree C. is 1463.

In No. 6, the LFP battery 40 Ah with electrolyte formula 6 has a self-extinguishing time of 18 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 2.86 mΩ and the charge/discharge cycle number under 25 degree C. is 1620.

In No. 7, the LFP battery 40 Ah with electrolyte formula 7 has a self-extinguishing time of 8 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 3.28 inn and the charge/discharge cycle number under 25 degree C. is 1335.

In No. 8, the LFP battery 40 Ah with electrolyte formula 8 has a self-extinguishing time of 3 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 4.37 mΩ and the charge/discharge cycle number under 25 degree C. is 1065.

In No. 9, the LFP battery 60 Ah with electrolyte formula 9 has a self-extinguishing time of 27 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 3.05 mΩ and the charge/discharge cycle number under 25 degree C. is 1517.

In No. 10, the LFP battery 60 Ah with electrolyte formula 10 has a self-extinguishing time of 17 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 2.56 mΩ and the charge/discharge cycle number under 25 degree C. is 1662.

In No. 11, the LFP battery 60 Ah with electrolyte formula 11 has a self-extinguishing time of 11 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 2.37 mΩ and the charge/discharge cycle number under 25 degree C. is 1918.

In No. 12, the LFP battery 60 Ah with electrolyte formula 12 has a self-extinguishing time of 8 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 2.69 mΩ and the charge/discharge cycle number under 25 degree C. is 1739.

In No. 13, the LFP battery 60 Ah with electrolyte formula 13 has a self-extinguishing time of 6 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 3.05 mΩ and the charge/discharge cycle number under 25 degree C. is 1505.

In No. 14, the LFP battery 60 Ah with electrolyte formula 14 has a self-extinguishing time of 14 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 3.18 mΩ and the charge/discharge cycle number under 25 degree C. is 1554.

In No. 15, the LFP battery 60 Ah with electrolyte formula 15 has a self-extinguishing time of 13 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 4.06 mΩ and the charge/discharge cycle number under 25 degree C. is 1258.

In No. 16, the LFP battery 60 Ah with electrolyte formula 16 has a self-extinguishing time of 10 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 2.32 mΩ and the charge/discharge cycle number under 25 degree C. is 2035.

In No. 17, the LFP battery 60 Ah with electrolyte formula 17 has a self-extinguishing time of 8 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 2.45 mΩ and the charge/discharge cycle number under 25 degree C. is 1906.

In No. 18, the LFP battery 60 Ah with electrolyte formula 18 has a self-extinguishing time of 14 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 2.63 mΩ and the charge/discharge cycle number under 25 degree C. is 1734.

In No. 19, the LFP battery 60 Ah with electrolyte formula 19 has a self-extinguishing time of 10 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 2.39 mΩ and the charge/discharge cycle number under 25 degree C. is 1895.

In No. 20, the LFP battery 60 Ah with electrolyte formula 20 has a self-extinguishing time of 11 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 2.15 mΩ and the charge/discharge cycle number under 25 degree C. is 2120.

In No. 21, the LFP battery 60 Ah with electrolyte formula 21 has a self-extinguishing time of 12 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 2.46 mΩ and the charge/discharge cycle number under 25 degree C. is 1887.

In No. 22, the LFP battery 60 Ah with electrolyte formula 22 has a self-extinguishing time of 13 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 2.43 mΩ and the charge/discharge cycle number under 25 degree C. is 1864.

In No. 23, the LFP battery 60 Ah with electrolyte formula 23 has a self-extinguishing time of 9 sec/g, an internal impedance ACIR (Alternate Current Internal Resistance) of 2.23 mΩ and the charge/discharge cycle number under 25 degree C. is 2117.

With reference to the batteries 1 to 3 in Table 10/FIG. 23A: the organic electrolyte contains 1% VC (Battery 1), which is considered as flammable electrolyte. The self-extinguishing time is 63 sec/g, and the internal impedance of the battery is 3.27 mΩ. The number of charge-discharge cycle is only 1359 cycles at the 0.5 C until reaching the capacity retention (C.R.) of 80%. By adding 1% FEC (Battery 2) and 3% EPFCP (Battery 3) in sequence, the self-extinguishing time is significantly reduced, and the long-cyclic performance of the battery tends to be slightly improved.

For Batteries 4 to 6 in FIG. 10 /FIG. 23A: 1% VC, 1% FEC, and then 5% PYR₁₃PF₆ are added to the organic electrolyte (Battery 4), the self-extinguishing time is significantly reduced compared with that of Battery 2. By adding a high melting point, low vapor pressure ionic liquid in the electrolyte, the self-extinction ability will be significantly improved but the performance of the overall battery drops. This is because PYR₁₃PF₆ ionic liquid is used and PF₆ ⁻ readily intercalate into the layered structure of graphite, resulting in a significant increase in the internal resistance of the relevant lithium-ion battery. In the Battery 5 2.9% HFCP is added as Stabilizer and in Battery 6 2.9% EPFCP is added as stabilizer. The self-extinguishing times of Batteries 5 and 6 are significantly reduced when comparing to Battery 4. The performance of the Batteries 5 and 6 have improved when comparing to Battery 4. Based on the test results, the addition of EPFCP as a stabilizer produce better results.

The Batteries 9 to 11 in FIG. 23A may be considered similar to Batteries 4 to 6 in FIG. 23A. By using DiPYR₁₅(PF₆)₂ as the ionic liquid with 2% HFCP or 2% EPFCP added as stabilizers, the self-extinguishing times of both are significantly reduced, and the performance of the Batteries have been enhanced. The use of EPFCP as a stabilizer produce better results.

For Batteries 6 to 8 om FIG. 23A, the organic electrolyte is fixed with 1% VC, 1% FEC as the film forming agents and 2.9% EPFCP, 5, 10, 15% PYR₁₃PF₆ respectively, or 6, 8, 10% DiPYR₁₅(PF₆)₂ respectively for Batteries 11 to 13. The self-extinguishing time for these batteries reduces by increasing the amount of ionic liquid added. However, the impedance value of battery increases with the amount of ionic liquid added resulting in overall battery performance. Therefore, it is important to find the optimal amount of A+B+C and it is a fine balance.

As to Batteries 11, 14 to 15 in FIG. 23A, it shows that the increase in the amount of film-forming agent VC will significantly increase the battery impedance, resulting in the poor performance.

With reference to Batteries 11 and 16 to 17 in FIG. 23A, by increasing the FEC content as the film forming agent, the self-extinguishing time is slightly reduced while the impedance value of battery remains relatively stable without significant increment. Among them, Battery 16 with 2% FEC as the film-forming agent shows best stability.

Batteries 16 in FIG. 23A, 18 to 23 in FIG. 23B show the best performance, with 1% VC, 2% FEC, 2.5˜2.8% EPFCP and 6% ionic liquid added to the organic electrolyte, with ionic liquid being a dual-core cationic chain or the aromatic bonded to cation according to the invention. Among them, the range of self-extinguishing time is from 9 to 14 sec/g, which is considered as a flame-retardant electrolyte. By adding an appropriate amounts of stabilizer and ionic liquid, a uniform and dense of SEI film with low impedance can be formed on the surface of the anodes which effectively reduce the internal impedance of battery to about 2.15˜2.46 mΩ, consequently enhance the performance of the overall batteries. 

The invention claimed is:
 1. An ionic liquid for adding to an electrolyte of a lithium-ion battery, wherein the ionic liquid comprises a compound with a dual core structure having the general formula (I): Z₁X₁YX₂Z₂ (formula I), wherein Z₁ and Z₂ are selected from the group consisting of PF₆ ⁻(hexafluorophosphate), POF₂ ⁻(difluorophosphate), BF₄ ⁻(tetrafluoroborate), B(C₂O₄)₂ ⁻(BOB⁻, bis(oxalato) borate), BF₂(C₂O₄)⁻(ODFB⁻, difluoro(oxalato)borate), CF₃BF₃ ⁻(trifluoromethyltrifluoroborate), (FSO₂)₂N⁻(FSI⁻, bis(fluorosulfonyl)imide), (CF₃SO₂)₂N⁻(TFSI⁻, bis(trifluoromethane)sulfonamide), CH₃SO₄ ⁻(MeSO₄ ⁻, methyl sulfate) and

wherein X₁YX₂ is selected from the group consisting of

1,5-[(1-methylpyrrolidium 1-yl) (triethylamine N-yl)] pentane

1,5-[(1-methylpiperidinium 1-yl) (triethylamine N-yl)] pentane

Bis [2-(1-methylpyrrolidinium 1-yl) ethyl] carbonate

1,5-Bis(1-methylpyrrolidinium 1-yl) pentan-3-one and

Bis[2-(1-methylpyrrolidinium 1-yl) ethyl] butanedioate wherein an overall amount of ionic liquid added to the electrolyte is 0.1-15 wt. %.
 2. A lithium ion battery comprising a positive electrode, a negative electrode, a separator, an electrolyte and one or more ionic liquid as claimed in claim
 1. 3. The lithium ion battery as claimed in claim 2 further comprising a stabilizer, wherein the stabilizer is a cyclophosphazene compound.
 4. The lithium ion battery as claimed in claim 3, wherein the stabilizer is selected from the group consisting of:

Hexafluoro cyclotriphosphazene; and

Ethoxy (pentafluoro) cyclotriphosphazene.
 5. The lithium ion battery as claimed in claim 3, wherein an amount of the stabilizer added to the electrolyte is 0.1-2.9 wt. %.
 6. The lithium ion battery as claimed in claim 2, wherein a SEI film forming agent is added to the electrolyte.
 7. The lithium ion battery as claimed in claim 6, wherein the SEI film forming agent is selected from the group consisting of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), ethylene sulfite (ES), propylene sulfite (PS), and ethylene sulfate (DTD), and combinations thereof.
 8. The lithium ion battery as claimed in claim 6, wherein an amount of the SEI film forming agent added to the electrolyte is 0.1-5 wt. %.
 9. The lithium ion battery as claimed in claim 2, wherein the electrolyte is a non-aqueous electrolyte; wherein optionally, the non-aqueous electrolyte comprises a lithium salt selected from the group consisting of LiPF₆, LiClO₄, LiBF₄, LiSO₃CF₃, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, LiN(SO₂CF₂CF₃)₂, LiAsF₆, LiAlCl₄, LiNO₃, LiPOF₂, LiB(C₂O₄)₂, LiBF₂(C₂O₄), LiCF₃BF₃, and combinations thereof; and wherein optionally, a concentration of the lithium salt in the electrolyte is 0.5˜1.5 mol/L.
 10. The lithium ion battery as claimed in claim 9, wherein the nonauqeous electrolyte comprises an organic solvent selected from the group consisting of carbonate, carboxylate, ether, ketone, and combinations thereof; wherein optionally, the carbonate is selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), dipropyl carbonate, dibutyl carbonate, and a combination thereof; wherein optionally, the carboxylate is carboxylic acid ester; wherein optionally, the carboxylic acid ester comprises at least one of methyl acetate, ethyl acetate, methyl butyrate, ethyl butyrate, methyl propionate, ethyl propionate and propyl acetate, and a combination thereof; and wherein optionally, the positive electrode comprises an active material being which is a lithium metal complex oxide compound.
 11. The lithium ion battery as claimed in claim 10, wherein a metal element of the lithium metal complex oxide is selected from the group consisting of a transition metal and a non-transition metal; wherein optionally, the transition metal is selected from the group consisting of vanadium, titanium, chromium, copper, iron, nickel and cobalt; and wherein optionally, the non-transition metal is selected from the group consisting of aluminum and manganese.
 12. The lithium ion battery as claimed in claim 2, wherein the negative electrode comprises an active material selected from the group consisting of soft carbon, hard carbon, artificial graphite, natural graphite, meso carbon micro bead (MCMB), silicon, silicon oxide compounds, silicon carbon composites, lithium titanate oxide, and metals that form alloys with lithium; wherein optionally, the negative electrode comprises an active material that is carbon-based, silicon-based or tin-based; wherein optionally, the separator comprises a membrane; and wherein optionally, the membrane comprises a material selected from the group consisting of polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), ceramic material, glass fiber and combinations thereof. 